...let's discuss one of the greatest philosophical debates in comic books.
On one hand, Batman's one rule is that he doesn't kill people, no matter what. He feels that it's not his job to be judge/jury/executioner, and he feels that if he makes an exception to his rule, he'll just end up killing more criminals and eventually be no better than them. Sliding down the slippery slope, as it were. Plus, if he killed somebody (even the Joker) Gotham PD would probably be on his back even more.
But on the other hand, the Joker is responsible thousands of thousands of people being killed, hurt, and tortured, including people close to him. This guy killed one of the Robins (sort of) and crippled Batgirl. He has no regrets about it and Arkham seems to be unable to keep him in jail permanently. Nor does Gotham seem to be willing to kill him. So it's probably reasonable to say that, as long as the Joker continues to live, he'll continue to kill/maim/torture people for fun.
So, assuming that Gotham is unable/unwilling to keep the Joker locked up or execute him...do you think Batman would be justified if he decided to just get rid of the Joker? Why or why not?