Do any of the folks in these bands even take the Satanic aspect seriously? I mean, how many even believe in a being called Satan? I would think the Nordic bands don’t believe in the Norse pantheon either. If God exists, I’d think he has a lot more important things to be concerned about than heavily tattooed people who sing like Cookie Monster and display impressive musicianship. I’ve got no problem with people listening to what they like; my sons aren’t into that kind of music but it wouldn’t bug me if they were.
**Deicide **certainly was claiming to be for quite awhile. Glen Benton used to talk about Jehovah being his enemy and Lucifer/Satain being his true god. He used to talk about killing himself at 33 like Christ, but that came and went and he is alive.
Here is Wikipedia’s summary of those times. I remember them in the 1990’s and early 2000’s and he was on about it.
Mayhem had a band member commit suicide. I believe they broke his skull into pieces to make a necklace or series of necklaces. It was talked about as Satanic, but I have no idea if it was.
And for good measure, here is one song from each.
Definitely the peak popularity of Deicide was the album titled after that song.
Mayhem was never very popular in the US, but here is their most famous song.
Old school black metal - yes, they take it very seriously. There is some debate between different factions, but for some, it’s Church of Satan-style vague Adversary and Social Darwinism, while for others it’s the actual Devil.
Newer ones may be more coy, and may be just attempting to be shocking, but may not necessarily outright deny any such belief.
Death metal bands are usually not as serious, for the most part. And the main theme is death, of course, not Satanism. The shock for the sake of shocking factor is stronger in other forms of metal.
Just Euronymous, and some of his band members and friends were appalled. He also took pictures.
How many church burnings have been associated with death metal?
An old co-worker of mine has a college-aged son, who plays in a Christian death-metal band. I can’t even wrap my head around that idea. 
Why? It goes back pretty far.
None, as far as I know.
A handful of Black (not Death*) Metalers in Scandinavia took the whole anti - Christian thing way too seriously and burned down some churches, and that inspired a couple of loonies in other parts of the world, but most of the fans of that style do not approve of that kind of thing.
*Yes there are important differences between Black Metal and Death Metal, enough that even someone like me who is no fan of either can tell them apart.
See: unblack metal. Not a big thing culturally though, as far as I know. The audiences don’t tend to mix.
My biggest rolleyes at “EEEVIL” imagery is the inverted cross.
I think it’s mostly just badassery. But King Diamond seems to be a consistent Satanist. And an excellent vocalist as well. Just don’t watch any of the old videos, they are a bit cringe-worthy. But I love the King Diamond and Mercyful Fate albums.
I’m a fan of both genres. The well known examples of Satanism have already been mentioned in Deicide and Mayhem, and the only more modern example I can think of off the top of my head is Behemoth, notably their most recent album The Satanist. But even that album is more about the adversarial nature of overcoming obstacles than actual Satanism. That said, there are a few random nuts who take it seriously, Varg Vikernes being the obvious example (formerly of Mayhem and Burzum IIRC).
That all said, as a whole, at least as it goes for modern metal, when bands take on the whole Satanism or Anti-Christian thing, it’s usually just a shtick. It’s not really all that different from a rapper pretending to be a bad ass gangster, in that it’s part of the imagery that has gotten wrapped up in the genre.
Also, most of this whole thing goes with Black Metal, as it is very theatrical in nature, not just musically, but with all the corpse paint, spikes, weapons, and what-have-you. I’d say the only other subgenre of metal that are similarly theatrical as a whole is Power Metal. Death Metal is generally much more straight forward, they’re the types that just wear black shirts, usually of other bands, and headbang; very little theatricality.
Certainly, he’s a nut. But he is one who has been consistently rather Pagan, in an extreme way.
Of the Church of Satan type, which is more philosophy than religion. He doesn’t appear to be just talking the talk, but his imagery has been more Salem Witches than Baphomet in my experience.