From Io9.com:
…the love of violence is really the main emotion that Kick-Ass expresses. Both inflicting violence, and receiving it. When Big Daddy points out that Kick-Ass’ superpower is getting his ass kicked, you can’t help accepting that it’s true. But the movie winks at us, through an eye that’s already swollen almost shut, and says, you know, that’s not a bad superpower at all. The broken, battered young body of Dave Lizewski is the most pornographic thing in the movie, and his contusions are badges of honor.
Superheroes don’t give us much in the way of lessons about morality, or science, or whatever — they give us a context in which violence makes sense. Much like gangsters, who are the other type of non-regular people we meet in this film. You could just as easily beat people up without wearing a funny costume or being a gangster, but then it would just be senseless assault. The superhero genre legitimizes our love of brutality. And our masochism, as I may have mentioned.
You can’t really love superheroes without being a painslut, Kick-Ass says. You can’t embrace all of the illogic and pointlessness and nastiness of men and women and children thwacking each other in shiny outfits, unless you’re addicted to hurt.
I think BDSM, like superhero stories, does depend on stepping into a sort of “magic circle”, a realm in which normal rules of society don’t apply, and the action is driven by less rational impulses. The problems come when the boundaries of the magic circle gets blurry.
Kick-Ass, incidentally, does have a power of a sort. Nerve damage from previous injuries reduces his ability to feel pain. This sets up an interesting question: wouldn’t a masochist NOT want to reduce the ability to feel pain? Or is just an excuse/reason to seek out even more extreme experiences?