Peter Parker got bit by a radioactive spider. Barry Allen, Wally West and Matt Murdock all had chemicals spilled on them. Bruce Banner and Phillip Solar were exposed to massive amounts of radiation. These are all things that would more than likely kill you.
Bruce Wayne and Frank Castle saw their family members killed before their eyes. Kal-El had his home planet destroyed. Odds are they'd be victims of these tragedies as well.
Super villains also tend to have similar origin stories. What if, for many, the Marvel and DC Universes are actually purgatory, where there choices and actions will purify them so they may enter heaven? That's why they never age, they never stay dead, and all of the world seems to be centered around them and their actions?
It's fun to think about, for a minute (but not much more).
Then the ethics in purgatory are more black and white than on earth. The good and the bad are really clearly defined.