Re: You Don't Have to be Crazy to be a Superhero, but it Helps!
My 2 cents.
Comic book mages deal with things that would drive most people insane upon their first exposure. I think of magical adventures as being like radiation poisoning. Mages have better shielding but some still leaks through over time. Also, as a mage becomes more powerful, he might become so attuned to mystic phenomena that his entire frame of reference shifts to that and everyone else starts commenting on how he seems to only speak in riddles and non sequiturs. It would make perfect sense to anyone who shared that frame of reference.
Putting on a costume to fight or commit crimes is, I think, an attempt to become more than just a human being. When a highwayman concealed his face, he didn't just conceal his identity. He also signaled that he couldn't be expected to conform to normal behaviors and could do anything, including kill at the drop of a hat. Batman is a classic example of symbolism to evoke fear of the dark, imo. Criminals accustomed to thinking of the night and darkness as their protector from the law had to rethink that when Batman loomed out of the shadows.
I agree that mutants just a metaphor for prejudice in most cases. There was a supplement called The Mutant Files that covered GENOCIDE and a mutant supremacist group whose name escapes me at the moment(IMAGE?). Anyway, it talked about a subset of mutants called the New Generation. They didn't have any obvious physical mutations other than being very physically attractive. Their package deal included extended lifespan, reduced need for sleep and stat bonuses. They were supposedly the result of the mutant genome stabilizing after the initial breakout and all of its variations. The implication was that they were the future of mutants on Earth (sorry, Beast, but you ain't it). It made me think of the Inhumans or some kind of proto-New Gods.