Even factoring this in, you don't need multiple stories to say the Joker should be put down. Writers go to great lengths to make the Jonkler le edgy and have him just spout out how he has skinned 100 babies before he does his next crossing-the-line act that should reasonably result in his death. Even my example, Injustice, is self-contained and has the asshole nuke a city, yet somehow Superman is wrong for shoving a fist through his chest. The consistent upping the scales to try to out-do the Killing Joke is why people think Batman should kill. That story already vaguely alludes to Batman killing him and that is for the personal crime of torturing Gordon. He has done so much worse since to not only Batman, but Gotham as a whole, yet seems to get less consequences with each round. The Killing Joke was supposed to be a final straw, a point of no return, not the invitation to scale up Joker it has become.