Re: If the author wanted a "killing is always wrong" shpiel, he picked the wrong villains.
I don't disagree that the Joker deserves to die, but I don't think Batman should kill him. However, I do feel that there are many alternate solutions.
A while ago, didn't Batman give Ra's Al Ghul some drugs that made him basically unable to move or talk? I don't think this is a good solution, its not really better than killing him, but I wonder why Batman doesn't do this to the Joker if he's fine with doing this to others.
My solution would be to have Zatanna brainwash the Joker. Sure, the last time she brainwashed villains, stuff wasn't pretty. However, she doesn't need to change the personality of the Joker. She just needs to go in his head and cure his insanity, which should be fine. Think of it as super-rehab.