
Manhwas and kdramas tend to show the elite/wealthy locking up their "troublesome" relatives in psychiatric hospitals, but they're not really, theyre just places for the wealthy to hide family members who could cause embarrasment or issues with their public image. It seems like that's what happened to him, if I remember correctly. Getting him treated properly would mean records of his condition, which would mean embarrassment for his father if it was ever leaked.

Only if they're taught. Psychopaths have no moral compass, they don't understand those things are wrong. He would've learnt later from media like news, movies, books etc, but without a psychologist explaining and guiding them on why it's wrong and why he shouldn't do them in a way he understands (usually through assessments by psychologists, this can take years to figure out what works), he wouldn't truly understand the *why*
You all need to remember that he is a literal psychopath. He doesn't understand love. He doesn't understand affection. All he knows is how his parents treated him like a monster and hid him away. Yes it was in a psychiatric hospital but it seems like the kind where wealthy families lock up their family members when they're an embarrassment instead of a place to get actual help. Most psychopaths are able to live proper lives if they're given proper treatment and stick to it.