LogFAQs > #976373027

It obviously depends on the character and what makes more sense.

Batman once murdered people left and right like a generic vigilante, then had to tone it down because it was for kids, evolved later into "I can't kill Hitler because then I'll lose my mind and kill everyone and take over the world", which was stupid, so that turned into "I tell myself and everyone around me some lie but in reality I'm only Batman because I'm afraid of other people dying"

Basically a plot device because Batman obviously can and should kill the joker, which is his main rival that they need later, so you have to make it his weakness for his character to make sense. Or, you have to make it so that he has some deeper wisdom than the other characters, which I think never works out.

You can see it at the end of Arkham Knight when Batman indirectly killed Ras Al Gul, finally growing as a character, and Ras tells him he's proud of him. That's a better version of his writing.