I'll also weigh my opinion in. Some of these heroes aren't like Batman. They won't just spare the Joker out of a moral code. Some [i]do[/i], however, but chances are, there's gonna be a war in deciding if Joker should be spared or killed.

Not to mention that there are a few bad guys who may want to ally with Joker and protect him if only to further their own deeds.