>>149092804 (OP)Super man *Avoids* killing. He doesn't not kill. He avoids killing because the entire point of his character is to represent hope. Striving for another, better tomorrow. And part of that hope is believing that you don't need to murder niggas to get your way. Superman restrains himself because he's a good person, but is willing to take the gloves off.
Batman doesn't ever kill because he's mentally ill. Bruce's entire worldview is informed by the fact that the murders of his parents must never, ever happen again. He puts these people in arkham because Bruce needs to think there's a way to fix them without murdering them, because he sees himself as no better than them. If he kills the joker, it'd just be another insane man murdering another.
Joker war, despite being a bit of a dogshit arc, did it best. You have the joker who KNOWS he could defuse the bomb, and batman needing to make a choice between chasing Harley, and letting the joker die. It's a more extreme version of the Jason Todd choice. And at the end, Bruce chooses Gotham over Joker, because Joker admits he's choosing his fate by not disarming the bomb.
TL;DR op is a faggot.