Okay. Here's the possible conclusion I have arrived at in relation to the extreme "belief" supposedly held by many in the metal genre...er...specifically the black metal genre. I'm going to be talking about the classic black metal right now. Mayhem, Emperor, Burzum, Satyricon, etc.
In early interviews with the bands, they all seem to express extreme views of hatred for humanity and such. Unless an individual is mentally disturbed/disabled, I do not believe that anyone can truly have these views. You have to put their comments in perspective. All of these people when they were doing and saying these things that have made them infamous were under twenty one years of age. I really think it's an age thing. I believe Euronymous was only about twenty when he was killed, but I can't find when he was born right now. Speaking of which, I would say that Euronymous is probably the most infamous, if you have read anything about the Inner Circle activities. If these things are true, I think Euronymous had some serious issues. But I really think that if he was still around to day, he would be doing similar things as Ihsahn is doing now.
So since all of these famous black metal people have grown up, they no longer seem to have these extreme beliefs. A few examples: Ihsahn...he's now a true musician, experimenting and making progressive music. Not that the Emperor work didn't show artistic ability, but he's not confined with in the black metal scene now.
Satyr of Satyricon seems to be losing interested in black metal it seems, from various things I've read. Satyricon have become a more commercial band and seem to have lost much of the musicianship and creativity present on their earlier albums.
Nocturno Culto and Fenriz might seem to be an exception to this, but for anyone that hasn't noticed, they're not really active anymore. Sure, we get the yearly new Darkthrone album....but that's it, aside from Nocturno's one recent performance at Wacken. And if anyone has read any more recent interviews with Nocturno Culto, it's also evident he has changed.
Now I do believe that there are real Satanists in metal, Akercocke for example, but I am using examples of the people who ten or fifteen years ago claimed to be evil, worship the Devil, and other such things. Yes, there are people who speak out against Christianity, believe in the ideas of LaVey Satanism, have Pagan beliefs, etc; But it doesn't seem to me that their are any truly evil devil worshippers in the black metal genre.
Now this is just a theory, and it seems to apply in a lot of places. But there are still bands such as Mutiilation who have remained relatively underground, and there is no reference to their beliefs except with their music, which still seems to be generally the same as their earlier albums. I'd love to hear comments from others on this possible theory, whether to aid or try to contradict it.