I give up on making it shorter. That series is 14 dense hours long, it covers a lot! And I have thoughts on some of it; you can also skip parts you are less interested in, judging by their titles.
I tried to avoid spoilers (otherwise they are marked)

1) Anhyun city: presenting postindustrial city through petit bourgeois ideology

When I talk about a friend group, I will mean two smaller friend groups of classmates as taken together: Audiophile group (the "goodies" of the drama) of Jae-Kyung + Yun-Jin + Joo-Song and the Won group of Jong-Soo + Tae-Jin + Chi-Hyeon + Yoon-Ho + Sang-Eui. Add to that the dead Jung Seo who bridged the two groups, as he belonged to both. I will call them all "friends" for convenience.

The story starts while focusing on Jae Kyung as an individual and his narrow subjective experience as a local cop. With each episode the perspective gradually widened as we were being introduced to more and more of his former classmates and ended up immersed in the web of their relationships in the past and now. But it didn't stop there and widened even further to include the whole city Anhyun and the radical transformation it underwent across the last two decades.

All the friends in our comprised group ended up belonging to all different stratas of society in the present time, so we can say that they form a microcosm of the city's society:
- chaebol's only heir Won Jong-Soo is a top capitalist class who "owns" the city, or rather its economic activity (his pharmaceutical company is basically a monopoly) and therefore has all the working people dependant on it and exploited by it;
- chief prosecutor Park Tae-Jin is a bureaucratic class, he can be even more powerful than the top capitalist class; despite being considerably poorer than any chaebol, this class designs everyone's life; a prosecutor is an unelected state official who can send anyone to prison (or at the very least make anyone's life a living hell for a long while) if he feels like it, and no amount of money maybe enough to save you;
- Oh Chi-Hyun is "muscles" of Jong-Soo, he is all those bodyguards and private security personal meant to protect persons and property of chaebol's class;
- Yoon Ho and Sang-Eui as working class of Anhyun city who have little choice but to work for Won Empire;
- Joo-Song represents small/medium entrepreneur-ship, a relatively free (as contrasted to monopolistic capitalist) market economic sector;
- Yun-Jin, obviously, represents journalism (or if broader, and intellectual class); it is depicted to be very corrupted and prone to taking bribes, though not for greedy reasons but rather for reasons that they are paid little and cannot even afford to support the smallest family; but their heart lies in uncovering and telling the truth;
- finally the main character Jae Kyung, a law enforcement officer, is presented as being self-righteous, tough and violent.

Upper classes
I also need to mention the Mayor, who is not part of the friend group, but in the series he is a representative of an elected state official (as opposed to non-elected beaurocrat Park Tae-Jin). Many are used to think of the top ruling class as homogeneous group with similar interests, but this story is really good in showing the antagonisms between every part of that group (that's why I found the baddies team more compelling than the goodies team, as relationship dynamic of a prosecutor Tae-Jin and chaebol Won family has a more real ground to it than relationship of a cop, a journalist and a small businessman, which are rather vague). Tae-Jin keeps close to Jong-Soo as a holder of capital, and Jong-Soo needs Tae-Jin's expertise and power as a prosecutor to be on his side to stay successful. Jong-Soo also needs to appeal to the Mayor who can approve or disapprove major development projects in the city, therefore close or open crucial opportunities to Won's expanding Empire. On the other hand, the Mayor can fall victim to the prosecutor's schemes, so it's not like he is invincible either.

Proletariat
There are 3 types of working folks in our friend group:
- Yoon Ho who clings to those on top as much as he can, but he is useless to them and also completely bonkers; when he is exploited and abused we don't feel much for him because he is THAT bad (for no reason);
- [mid spoiler]Sang-Eui is a smarter one; he has all the right ideas about who are villains and who are victims and understands well what is going all (has recording device on him at all times to spy on his superiors), but he is blinded by his radicalism (they call it by euphemism "obsession") which makes him too bloodthirsty and dangerous[end of mid spoiler] ;
- Jung Seo is the main victim; he is the one who was pushed into black market, which eventually killed him

As you see, the working class is either villains or victims (including poor characters outside our friend's group, with those in the black drug market being villains, while those being just poor are victims waiting to be saved by the goodies team), which is standard for petit bourgeois fiction.

So far we covered villains and some victims. Out of three goodies characters (Audiophile team), who do you think is the real hero? An entrepreneur Joo Song! (doesn't matter that he has the least amount of screentime or stuff to do) It's through his small scale business, Two Star Holdings, late Jung-Seo signs up for an insurance plan that after he dies will help the other two, the detective Jae-Kyung and the journalist Yun-Jin, fight their demons (for Yun Jin - quit running for the money and devote herself to truth, while self-righteous Jae-Kyung will be humbled down and warmed up towards people with flaws he previously despised, ending his excessive violence) and bring forth their best qualities to solve the mystery, punish villains and restore good order in the city. And if successful, be generously rewarded for that financially. Insurance is like both a guiding star towards the right path and a reward for following it.

Interesting to note how the top capitalist class is presented like it's new aristocracy, how often it's emphasized that the only one who can inherit Keumhyung Pharmaceuticals (postindustrial monopolistic company that mirrors the Estates of feudal times owned by a particular noble family; current stage of capitalism is seen as neo-feudalism) is the biological son of its owner, Won Chang-Ho. Despite how much Tae-Jin did for the company and how much better he is qualified for the job than incompetent Won Jong-Soo, the latter father's ultimate goal is for his son to inherit his empire. Another major sign of feudalistic aristocracy (apart from owning a whole city with its working force + inheriting all it by birthright) present here is a professional personal armed force (ok not so armed, they can't carry a gun, so just muscle force) that I already briefly covered.

When Jong-Soo reflects on what went wrong, why some mere mortal like Jung-Seo caused him and his fathers' company so much trouble, blurred hierarchical lines were to be blamed. Tae-Jin treated Jung Seo like his equal partner in business and that gave Jung-Seo too much power (guaranteed by owning the other half of the password for cryptowallet, basically giving Jung Seo equal access to money they earned together, and not like it usually is, employer having all the profits and than deciding what crumbles their employees will get from this) and too much self-confidence, so much that he had the audacity to demand to be treated with dignity and fairness, and had actual tools to pressure his superiors with.

Also notice that only in the area of black unregulated market Jung-Seo was able to negotiate an equal treatment and fair distribution of profits. Because all legal institutions of modern capitalist states are designed to favour and uphold the power of monopolistic companies while keeping their workers in a much weaker position. In the legal framework, Jung-Seo can only beg Jong-Soo on his knees for charity and then receive rejection anyway.

2) Сopaganda and beyond

Here and there there are instances of primitive copaganda. I call them primitive because they are easily recognisable and can be separated from the rest of the story without affecting it. Some of it looks like something that was added because the channel needed to have the copaganda to be there explicitly in the show about cops and war on drugs, and I assume it was not part of an initial idea of the writer (on her previous project she worked with Lee Sun Kyun, an actor who commited suicide after being prosecuted on the charges of drug use, so I tend to believe her intent was to draw attention to the ills of drug criminalization). Nevertheless, it would be wrong to just ignore it like it's not there, so I will list those I noticed and consider most significant:

- the scene that exemplifies official conservative copaganda "reasoning" happens in the beginning of the last episode, and it is quite nauseating what it tries to promote. One of the police officers was caught for conspiring with leading drug dealers in the area, and when our main character, Jae -Kyung, asks him why he did what he did, the officer explains that just catching drug users isn't effective (here he is right, it's completely ineffective, though it won't lead anyone here to think of decriminalization), so he thought to cooperate with the dealers and get them move somewhere eventually and this way clean their district from drugs. To answer him, Jae-Kyung gets into his self-righteous mode and explains that their work is hard, and maybe ineffective (he was that close!..), but they need to keep "cleaning garbage (!!!!!)" from streats, because that's their job to do, closing like that the argument that ig was supposed to represent the debate around drug policing (obviously, the real debate and issue with war on drugs is not like that at all). Not treating people like garbage, stop incarcerating them and harassing them and instead providing them help if needed isn't even an option in the cops' paradigm.

- the show contains casual use of derogatory language like "dr*ggie" and "j*nkie* (I obviously don't know the original Korean words used, that's from English subtitles, but I assume that were a derogatory words since it were translated like that), ending with total dehumanization by calling drug consumers "garbage"; one time an officer on their team mockingly mimicked stereotypical image of a an addicted person, like illness (disability?) was funny;

- we see police officers repeatedly and casually harass, belittle and threaten those they persecute, which is depicted in an unproblematic fashion (in contrast to scenes of cruelty inflicted by any other group, which is always portrayed in explicit negative light); in the least cruel instance Jae Kyung is shown to pressure an incarcerated drug user into incriminating others (who are his friends) by denying him access to certain food he cannot attain in prison and, more importantly, taking away additional phone calls; the other time they coerce previously jailed person (by threatening to persecute him again even though he tries to do legit business this time) to reach to his old contacts in the underworld and force (the only condition cops give is "don't get them into ER", technically meaning they can be as good as dead as long as it's not documented) them to share a certain information; and the other time our cop heroes plainly threaten horrible death to another incarcerated person until he opens up and outs certain people he knows in the black market.

It all sounds pretty grim, but I cannot help but notice, that if you abstract from the way it is filmed and framed and imagine only how scrip text might have looked like, you will see that the police isn't painted that positively, and by depicting all that violence the writer actually exposes real issues with the police force, highlights the way they see their own role in a society (heroic) and their attitudes towards people they persecute (dehumanizing).

In that sense I especially want to point out how we are introduced to the police narcotics team department the main characters serve at. One illustrative scene is from the 1st episode, when the team gathers to celebrate Jae-Kyung's promotion. The thing they argue about the most is whether the bull was slaughtered right before it was cooked and served (as they would prefer the most) or a day or so earlier (which would make the meal less exciting and desirable). Even though it is filmed as a fun bickering, the uncanny feeling comes through. Having seen right before that like Jae-Kyung used excessive force to avenge a culprit (making him disabled for life) and then smoothly avoiding any responsibility and instead being rewarded with a promotion for catching the dealer, and now hearing the talk about desire for a slaughtered animal, all that successive chain of events paints the police officers as violent bloodthirsty predators. And when Jae-Kyung becomes addicted and then has to swallow his own blood to destroy test samples, he becomes a predator preying on his own body, a vampire sucking his own blood, because as a drug user he is now, by definition, his own target to catch and devour.

3) Depicting drug dealers, drug users and battle with addiction

From my brief survey, the general professional consensus on what can help people with addiction are 1) having those who love and support you around, 2) access to a professional medical treatment. If you criminalise drug users, it cancels both, as incarcerated people lose access to their loved ones and are put into a hostile environment when they are routinely harassed and abused (basically, treated like "garbage" as Jae Kyung calls people he persecutes). And, obviously, they won't receive the medical treatment they need in prison. While drug users who are not yet incarcerated cannot get medical help because it will expose them to authorities as drug users and will get them incarcerated.

Those who enter an illegal drug market are people whose entry into the legal economy is closed off, while black market offers some considerable income. But for that the participants have to pay by dangers (aside from dangers being incarcerated) created by the fact that in the illegal area they have no access to legal protection, and that leads to many internal conflicts being resolved by violence. [mid spoiler]We can see it in an example of Tae-Jin, who can get funds to invest in a major capitalist enterprise only through quick and enormous profits possible on the black market. We can see it in the example of Jung-Seo, who also can gain money for his daughter's treatment only through black market as well. And when the conflict emerges, none of them can turn to legal protection, which leads to violence within the group.[end of mid spoiler]
Since the showrunner's policy seems to be committed to demonising and victimising the poor, the lower class participants of the black market won't be directly tied to systemic causes of their behaviour. Petty dealers and lower class drug users are depicted stereotypically evil. But if you pay attention to the overall worldbuilding of the story, it won't make it hard to make necessary connections between impoverished (by the Won's family developmental project of building a highly modern postindustrial city out of rural town in only 20 years by methods of fraud and coercion) inhabitants of Anhyun and their entering illegal market area as the means of survival, mirrored symbolically in Jung-Seo character, who represents both
-the dealers: he is pushed into working in illegal market as the only available way to make money for his family member to survive;
- and drug users: his daughter who needs special treatment but whose access to it was concealed by an upper class represented by Jong Soo who closed off the possibility of medical coverage by insurance.

And this is a very typical scenario in an invention of masses of people addicted to drugs who are then criminalized for their addiction: a legit pharmaceutical company prescribes legit drugs to lots of patients, then those drugs are prohibited at one point, and patients (some already addicted because they used the drug prescribed to them, some not yet addicted but knowing the drug would help in their situation when there are no other alternatives, esp after the insurance companies are also prohibited to cover certain treatments) simply have no other choice then to turn to the black market. And since that market is unregulated, drugs are of poor quality, doses hard to measure, which results in lots of serious health risks, as well as overdoses and deaths (which are almost absent in cases when drugs are legally available).

So we see this scheme euphemistically told in the series too. Both through how the Lemon Mulberry drug got to be invented (by legit pharmaceutical company), and then distributed and sold (black market invention), and through Jae-Kyung addiction journey, which was not voluntary (and no addiction is, despite primitive propaganda elements of the show trying to tell you otherwise), and then whose medical treatment was hampered because he had to keep his health issue secret to not be locked up. [spoiler] Later, when his secret becomes known and luckily for him he was admitted to be innocent and got an opportunity to receive professional treatment (what should happen to all suffering addiction, instead of incarceration), he was finally able to effectively manage the problem and lead a normal life.[end spoiler]

Note how much the supporting presence of his friends was crucial for him to stay afloat (when he was completely alone it was close to impossible), that crucial connection for those battling addiction that incarcerated people are denied.

I also appreciate the series drawing attention to the fact that (in South Korea at least) one cannot take samples to test for drug traces in someone's body without the consent of that person. In first two episodes, Jae Kyung simply destroys the samples taken by hospital staff from him (it is said to be a common practice which must result in lots of people locked up, especially those ignorant to their right to deny consent to testing) and then explains how his rights were violated, this way also providing rhetorical tools to defend themself for viewers who might occur in similar situation.

In another instance we also see how Jae-Kyung is able to get at least some treatment without outing himself as a drug addicted person, and that is when he asks Yun-Jin to go to a doctor and get a prescription for certain weight loss medicine (intended for diabetics) that is believed to help somehow with addiction too. Yun-Jin is very slim and it's clear she doesn't need weight loss, so without literally saying that she is a drug addict she (un)subtly signals the doctor that she is one, after which the doctor prescribes her the medicine. After that experience Yun-Jin feels very bad because she had to pretend to be an addict, this way the show also implicitly commenting on an enormous stigma drug users suffer. Yun-Jin got to be an addict for 5 min and in front of just one person, and it significantly crushed her spirit for a while.

4) Back to the narrative story

A tragedy that happened 20 years ago with the truth concealed and justice averted resulted in the participants' inability to grow out from infantilism and mature, leaving them in a perpetual state of adolescence's confusion, vulnerability and senseless cruelty. Jae-Kyung never learned to forgive and accept flawed human nature, which made him merciless and lonely. Yun-Jin lost her high morals and ideals, Jong-Soo never learned to take responsibility for his actions, Tae-Jin never got to know and forge relationships that are not transactional but genuine, and Sang-Eui was never able to handle rejection. Guilt-ridden Jung Seo, on the other hand, couldn't accept his own flaws and ability to inflict harm on others that he wasn't always able to control, which turned him careless toward himself and opened to easy exploitation by others first, and prepared for martyrdom later.
The place of Jung-Seo's death being the same as the place in which their classmate died 20 year ago not only underlines the direct connection between the two tragic events, but also bridges interpersonal tragedy to the history of the city as whole, as what previously was a family home of their classmate Kyung-Tae now was turned into a construction site that expands Won's industrial Empire. Previously a rural city of Anhyun filled with small scale farmers was symbolically burned down with its inhabitants (just like Kyung-Tae's home literally burned down with his body) in order to become a possession of a single family who built their postindustrial city on people's corpses.

The fact that Jung-Seo body fell in front of the eyes of his upper class friends right when they were gazing over the Pilo-Dong district (the one remained "undeveloped" part of the city they were planning to get their hands on) also emphasises the direct connection between expanding capitalist's monopoly and all the lives that won't be spared for the sake of "progress" (symbolised in the innovative Bioindustrial Complex project) brought on by it.

The peculiar balance of the Won's friend group is sustained by having someone at the very bottom that all of the rest can exploit. After that target to channel all the work, frustration and violence onto is broken and gone, the internal struggle intensifies, ending with assigning the most inferior position to a new member, and the cycle of abuse repeats as more and more members are used and utilized, and a devouring machine moving upward, inevitably reaching the ones at the very top who at the end cannot carve for themself even the narrowest safe space.

Defeating that (self)destructive system and coming back to the initial happy state vaguely remembered (fantasized?) from the times of childhood's innocence is imagined to be possible only by going way back into the past, to the original moment of transgression and trauma, unraveling web of lies and unearthing the long buried deep down truth, after which Justice can be finally served and release all the participants from their agony. When innocence is gone it's gone forever, but that loss opens up the road to maturity, a state more knowledgeable, and that is still within reach.

main sources consulted:
Alex S. Vitale "The End of Policing", chapter on War on Drugs
Wikipedia article "Drug policy of South Korea"
And I borrow the distinction between more free market capitalism and monopolistic capitalism from Immanuel Wallerstein "World-System analysis"