A Batman who doesnt kill is the equivalent of a Superman who does. His refusal to kill is completely flawed because he is not protecting anyone in Gotham City by allowing his enemies to live and throwing them in jail doesn't help either since they continue to break out of jail and terrorize the city. More and more innocent people will get hurt or killed by these maniacs because Batman is unwilling to do what is necessary which is why in the Dark Knight, everyone in Gotham City is blaming Batman for all the Joker killings and for not killing him when he had the chance. Just hearing about his no-kill policy makes Batman out to be an angel who pretends to be a demon which is giving me second thoughts about being a Batfan.
And in a way, you prove my point from a few pages ago about how much the no-kill rule defines this character.
It's a fact most superheroes don't kill. A lot of those superheroes fight more dangerous threats than Batman does, like gods and aliens. Yet despite that, you don't seem to be disturbed when those other heroes keep their villains alive, and even support the stance that Superman shouldn't kill. That's because even if you don't agree with superheroes not practicing capital punishment, it's still a peripheral part of their character most of the time. A peripheral part of superhero culture that was originally implemented by censorship. It may not go against their characters, but it also doesn't define them in a grandiose way. So your mind is able to ignore it.
But with Batman, your mind ceases to be able to ignore it because the rule has become such an engrained part of the character to the point you can't separate it from him without radically changing him, so it disgusts you and turns you away. No one has had their no-kill stance as often challenged as Batman did, and what you brought up is a huge ongoing theme in many Batman stories. That's why a Batman who kills is the equivalent of a Punisher who doesn't. You can't have that, it is what
makes him Batman.
As for the argument you proposed, I feel the need to point out there's nothing wrong with applying Bruce's morals in real life. In the DC Universe, criminals breaking out and causing havok is weekly universal procedure for all villains, not just Batman ones. In the real world, the Joker would be thrown in prison and stay there, maybe breakout once or twice in a lifetime
at best, but definitely not all the dang time like in the comics. Comics do that so writers can have the opportunity to reuse great villains and keep sales going. In other words, it happens because the Joker sells.
Thus if you kill him off, and by Batman's hands, he'll still return not too long after and just continue his gig. What then? Does Batman kill him again? Only for another writer to come along and want to use the Joker, then bring him back and kill him again? Is Batman then in the srkng for not crossing other boundaries and, say, sell him as a slave on Apokolips?