Gotta remember Charlie Manson was way into the Beatles Helter Skelter so it isn't just metal that has evil. Mozart was called satanic by some during his day, and of course tons of blues musicians have been labeled as such.

The fear of the evil and satanic is part of their marketing though. I have zero doubt of that, though it is really not my thing either. I am trying to approach the series from a scholarly perspective and not bleed too much of my own bias into the sub-genres I don't care much for.