New Brevoort Formspring

“If the Joker is caught and tried by a jury of his peers and given the death penalty, well, that’s the state, the system, deciding that such a punishment is fair and just. Anything else is a unilateral decision, and simply murder—especially if the Joker doesn’t pose an immediate threat to the person in question (such as, say, Batman.)”
And of course, the most important thing is this - the whole point of Spidey or Batman is that they have the opportunity and the ability to ignore that high moral imperative, and never do. They always seek a better, more hopeful way. That’s why they are heroes.
Its the same restraint that stops Superman ruling the world ‘or everyone’s benefit’, or the Flash resetting the timestream wheever things go tits up, and it contrasts with characters like Venom, Doom or Kang who DON’T have that restraint, and are not as heroic, regardless of the purity of their motives.

Cheers, Darryn