this   the whole thing about good vs evil, good is harder to do, you need to think about your actions, consequences and then act.  evil is turning off your brain and acting on instinct. hate someone? kill them, beat them.  that's why sometimes killing is righteous, when you're thinking about protecting someone, doing something right. just confess the sin of killing afterwards. haven't read assassination classroom, but if the manga is just about the thrill of killing, or doing it as a way to achieve more power, it's brainwashing for younger children. as an adult, when you understand the concept if good and evil(some still don't) then you can read it.  bible is about teaching yourself to differentiate between good and evil. realize the evil and say no.   funny you mention that book, the brothers karamazov is a great example of above. good vs evil and the struggle of within yourself to do better.
Canada