Yes it is. But I think often its treated as an artistic genre thing, rather then religious. It is anti religious with dark macabre sentiment. Rather than actual theistic satanism in a faith based sense. Or, its philosphically calculated, like "I am liberal, and so - apparently - is satan, so satan is the good guy." Also, I think the metal crowd want early revenge for being told they'll be sent to hell in the future, so they are messing with peoples minds - youre in hell now and satan is my lord, forget the after life, this one matters and metaphysical revenge (i.e my toying with your categioriesto my dark advantage rather than yours) ... "early karma" for you baby, revenge is sweet. Its a artistic exploraiton of the dark side in other words. A bit childish perhaps. Pensioners usually prefer opera maybe?