There's a reason why the law put mentally unstable people in mental insitutions instead of jail, unlike psychopaths, they didn't choose to be like this, it's either they let go of their emotions or they suffer more, that's what the human brain does when it's under constant attack. Sangwoo had nobody, no friends, no family to care about him and no one to teach him the difference between right and wrong. What did you expect? Him turning to an angel when he grows up? He witnessed his mother murder and bury his abusive father for gods sake, i dare you to tell me you wouldn't go fucking insane after going through all this!!!!
No, i wouldn't. Why would i sympathize with a person that unleashed all of his pain on someone elses? Okay, you go through something like this and not snapped. But what's Sangwoo excuse?
Heck, someone go through something worse than him and yet they don't want someone to go through the same thing. Nobody fcking expect him to be an Angel. Are you serious? Why did you think there's only two options, mental institution and prison? He can get both. And yes we put people mental in institution, but Sangwoo stepped too far already. The moment he kill a person. That's it. Jail is his destination.
Psychopaths are born, not made and they have full control over their actions, and despite the popular perception, most psychopaths aren’t coldblooded or psychotic killers, they're just unconcerned for the feelings and safety of others so it's entirely their choice if they want to commit crimes. Sangwoo was not born a psychopath, it's the environment he grew up in and the abuse he suffered from both his parents that made him like that. No childhood abuse victim turn out mentally stable when they grow up, it depends on the intensity of the abuse, some of them have trust issues and difficulties forming healthy relashionships with people and connecting with them, others either go insane or become apathetic. Apathy is a lack of feeling, emotion, interest, and concern. So an apathetic Sangwoo who doesn't know or care about right and wrong does what he grew up witnessing so it's not entirely his fault. No i'm not defending his actions nor support them but i do not want him to go to jail because i'm certain and sure that if Sangwoo grew up in a different environment everything would've turned out differently and he would've been a healthy mentally stable person. And fyi, a mental institution would not help him 100%, what happend to him is not easy and it would affect him the entire rest of his life, but he would at least regain some his sanity back and be able to function as a normal human being.
What's his excuse?!!
1- Suffered from verbal, physical and mental abuse from both his parents till their death.
2- Suffered from environmental and emotional neglect during his childhood. ( no one was there for him to teach what's wrong and what's right."he grew up seeing his parents abusing each other so what's wrong with him doing the same?").
3- Witnessed his father abuse his mother. ( him abusing others is a learned behavior ).
4- Witnessed his mother kill his father. ( "so if his mother does it without remorse than it's not as bad as people make it seem and he shouldn't regret doing it either")
So basically he knows no sence of right or wrong, only what he learned through his parents. I don't think that Sangwoo even fully knows what he's doing. He doesn't consider killing people a bad thing but he knows there's something wrong with him but he doesn't know what it is, in the last pages of chapter 27 he said that he doesn't want to be like his father so he knows what his father did is wrong but he knows no other way to act than what he was taught.
Why would you sympathize with a person that unleashed all of his pain on someone elses? You wouldn't because you don't understand, not even i do. What i'm going through is not as half as bad as what he has been through. My mother never killed my father, cancer did. And i'm not saying that Sangwoo shouldn't go to prison, because he should punished for his crimes but i'm sick of people not acknowledging his mental illness. Watch the documentary child of rage on youtube and you might understand a little better. This is what would've happend if Sangwoo got treatment during his youth like this little girl.

It's suposed to be Sangwoo x Yoonbum x MentalInstitution. You haven't been through the physical, verbal, emotional or mantal abuse Sangwoo has been through so you would not understand even if you try. But growing up in an environment like that it's inevitable that you become mentally unstable. Trust me i know, i'm going through almost the same thing and the only reason i haven't snapped already is because i'm too selfish to ruin my entire future for people who hurt me.