If heroes killed all their enemies, they'd have no one left to fight.
End of comics industry.
Not necessarily true.
Take a look at comic magazines' father, the pulp magazines. The Shadow killed villains, but some of them could escape and return, like Shiwan Khan. On the other hand, Doc Savage treated his foes with brain surgery, which was so successful that only one or two of his foes returned to crime. Yet, both titles lasted for more than a decade, and at least The Shadow was popular enough to 'survive' WWII and its paper shortage.
"Batman is only meaningful as an answer to a world which in its basics is chaotic and in the hands of the wrong people, where no justice can be found. I think it's very suitable to our perception of the world's condition today... Batman embodies the will to resist evil" -Frank Miller
"Conan, what's the meaning of life?" "To crush your enemies, see them driven before you, and hear the lamentations of their women!" -Conan the Barbarian
"Well, yeah." -Jason E. Perkins
"If I had a dime for every time Pariah was right about something I'd owe twenty cents." -Ultimate Jaburg53
"Fair enough. I defer to your expertise." -Prometheus