Call me a cynic but it's ALWAYS about the money and creating a gimmick to market yourself.
Ozzy didn't bite the head off of a bat because it tasted good. Sure he's a crazy mofo to begin with but
Alice Cooper couldn't be any more normal. My dad played golf with him in Maui. I got to ride along. All about the show. Biting the head off a chicken and drinking the blood on stage
Satanism is their gimmick. Appeals to a big group. They may believe it on some level, but it ain't the real thing like Charlie Manson
Some of these guys are just naturally F Ed up human beings but that just makes them that much easier to market!
So at least two guys are in for Slayer, Amendes and Gryzz, who else?