I respectfully disagree 100% and believe that to have Batman (and later Superman on the last panel of Strikes Again) give in to killing makes him just like all the others and it is the laziest possible thing to do. Miller wrote an absolutely ridiculously unrealistic and lopsided world where no matter what, Joker would get out and murder again no matter how many times he was brought to Justice. He backed the reader into a corner, forcing them to accept that killing the Joker was finally necessary and you'd be a naive moron not to agree with it. It's extremely forceful of Miller to shove his view down the reader's throat and openly spit on the "no-kill" rule of the two biggest icons in comic history. Life isn't as cut and dry as murderer goes to jail, breaks out, murders again, goes to jail, is released on technicality, murders again, forever and ever. How is it all that different from Marv killing the evil priest because he's sick and needs to be killed and there is no justice system that will hold him because of technicalities? It's just Frank Miller taking an iconic character, removing the ideals that he personally doesn't agree with, and forcing his own onto the character in their place.