There's "Satan Worship" and there's "Worship of evil". The first is basically a reversal of Christianity. The second requires no Christianity or belief in anything other than evil.
And Sorcha, I agree completely. That's a large part of why I get irritated at so many of the people who "do the Goth thing". You're definitely right about self-mutilation--it's not funny, it's scary. People who do it have a lot of pain they're trying to cope with and need help with that pain.