^They're the good guys, they aren't in to the whole murder thing.
That star spangled Theymiscrian girl they hang around with, not so much.
IMO by NOT killing the Joker who kills, kills and kills again Batman is borderline aiding and abetting him. He should just kill him to save his (inevitable) future victims.
OK, and so is Commissioner Gordon, every judge, jury, psychiatrist, jail guard, nurse, janitor, etc etc who has any opportunity to kill the Joker.
It's great to argue Batman should kill the Joker, but then what? Does he kill every villian that looks like they might kill someone someday? And then what happens the first time he makes a mistake and kills the wrong person? Or kills someone that could easily have been cured?
If you really want to advocate Batman as judge, jury and executioner, then why not advocate that role to every cop on every street in real life, think of how many innocents would be saved? Except we'd be living in worse than, oh excuse me, I was about to invoke Godwin's....
So we could make an exception for the Joker, who has proven time and again that there's no hope for him, he will always escape, he will always kill, and he will kill in a way that hurts the survivors as much as possible. Thing is, that's Bruce's choice, not yours. If you want to put on a stupid black suit, grab a gun and call yourself the Punisher, that's your choice, but for Bruce it's his choice. It's not just a question of how he's written.
For Bruce to suddenly kill, he has to change, he has to decide that he has been wrong all of his life, that his previous reluctance to kill was pointless and wrong. That is not a decision that's as easy as choosing what sandwich to eat.
Bruce is not responsible for any of the Joker's victims, not in any logical, ethical sense. He is under no obligation to kill anyone, any more than you or I are under any obligation to kill anyone. When he puts on the cowl and buckles on the belt, he has to make his own choice on how far he is willing to go and still be able to live with himself. He makes that choice, not you, and it's not up to anyone else to hang the blame for any deaths on his shoulders, any more than I hang the blame for any local gang deaths on the neighbourhood constable's shoulders.