because he never felt the love of a real family/ parents, never properly taught a lesson (life lessons like manners, love your fellow man, learn to socialize, etc.), and especially he is schizophrenic and never been seen/treated by a psychiatrist ( it really is so hard to have schizophrenia I'm telling you man especially he's just a child) so it's no surprise that he became like that, his actions are actually not all by his choice and decision since he have mental illness that he didn't even maybe knew he has. I'm not on his side but after understanding his pov i literally can't fully hate him.
depressed reader.
