Um...metal artists (especially black and death metal - imagine that) have been known to do some really crazy things.
Edit: Read your explanation. Just because someone calls themselves a "gangsta" doesn't mean anything, when a lot of the time it's just posturing to sell an image.
Uhm... there's a huge difference between black metal bands who've burned down churches and a commercial watered down hard rock band. There's a much smaller difference between rappers who commit crime and rappers who don't but rap about it. In fact, many come from the same scene.