Why hasn't anyone tried to be superhero?

Unless you're bulletproof you'd end up dead. Kevlar can be easily overcome by APS rounds which are readily available. Piss enough people off and someone will come gunning for you. And even if you did manage to catch the bad guys (without killing them) they'd end up walking out of court free men due to the f-ed up legal system. But if you did kill them then you'd be accused of murder even if you claimed it was in self defense. Finally, you'd have the media falling over themselves to find even your slightest fault and blast you for it. It just doesn't pay to be a superhero and that's why you don't see them.