Although I understand the logic, I don't see the ending being about reality but rather being about morality. If we are talking about cruelty, misery and realistic world, this ending is actually quite the opposite of it.
The hero shows up and saves the day and get's his life restored. The bad guys die in the end. The good wins and the evil is defeated. Truth is that the author probably felt the pressure to kill Sangwoo instead of letting him live or even more, get away with it. People demand 'justice' to fix reality --- the author would probably be harassed if she had dared to give KS an ending where the murderer goes free and living and the detective dead. That would be actual more reflective of reality. We got a fairly cliche 'hero wins, bad guy dies'.
Except there is no good side and no hero in KS, they're all flawed and tainted. Your interpretation is a bit skewed, this was not about a serial killer getting caught and getting punished, this was about hurt, broken people whose life went off the tracks at some point and they never recovered. And for these types of people there is going back and no happy ending. Sangwoo was always going to die. KS was not about him as a serial killer, it was about his constant fight with his demons and ghosts of his past. And it was a fight he was never gonna win. This was about the tragedy in people's lives, it was not about the fight of good vs. evil. And yes, this ending mirrors reality, there have been and always will be Sangwoos, Bums and Seungbaes in the world with similar backstories. Your scenario is not entirely accurate because evil people don't always win, they do caught and they do get punished, you are much too cynical. Also, don't presume to know how the author intended to finish her work.
Exactly.
You are right but just a thing, Koogi said in an interview that KS is actually a story of a serial killer and Sangwoo represents her idea of a serial killer.
Yes, but the point I was trying to make is that the focus is not on his serial killings, but his tortured mind and what led him to it.
It's easy to say it was a cliche "hero wins, bad guy loses", but the truth is that Sangwoo was already a violent serial killer and on a downward self-destructive path when he imprisoned Bum. The reality is that there is no pulling up given that kind of situation. Bum might've had a chance, but Sangwoo purposely made sure to drag him down with him. It was a perfectly logical progression of events, and really no one won in the end (except the old lady who just wanted some peace and quiet).
Honestly I liked the ending. It felt so real, Bum feeling out of place in the normal world, Sangwoo dying horrible death and just ..reality. Reality with all its cruelty, loose ends and all around people not caring for each other.