GoD's argument is based on the idea that the genre itself is a separate entity from the bands that constitute it, who are subject to its ideological principles.
Or rather, that all music is the product (the aural expression) of the creator's mindset/ideology, and that the inherent, defining element of death metal art from the outset was always that it strips away all external symbols and focuses on chaos and death.
I tend to operate on the opposite assumption; i.e., the genre is shaped by its constituent artists.
This seems paradoxical to me - it's a viewpoint which begs your own viewpoint. I believe the genre is shaped by its constituent artists, and that artists who express things incongruent with death metal are not death metal, in sound or in anything else. If they express things congruent with death metal in sound, yet throw Christian lyrics on top, they're simply not really sure what they're doing (or they're joking).
Genre is a difficult concept, and while it can be useful in cataloguing and recommending bands it too often gets in the way of accurate description and (all-too-often in the metal community) leads to conflicts over who is the most grim tr00 necro kvlt, and who is a "poser" (black metal, i'm looking in your direction).
I agree, though it doesn't seem relevant.
There are some who believe Christianity is incongruent with their vision of death metal (or whatever genre), and others who justify a connection.
Far, far more in the former category, with good reason. Note that sound has evolved a certain way since the beginning of music, to mean certain things when composed in certain ways. DM, being the blatantly anti-populist genre that it is, as well as being closely related to black metal, and focusing on death (which Christianity essentially masks), etc... everything points to it being non-Christian.
However, as I see it those genre boundaries are man-made to begin with. There were bands, and specific "scenes" (e.g. the notorious inner circle), formed with specific goals, but who is to say whether those specific individuals represent the "true essence" of the genre? I mean, look at Varg, his beliefs have changed over time but would anyone accuse him of being a "poser"? Can he currently hold different beliefs than those of the original circle and yet at the same time remain true to the goals supposedly set in stone for the genre of black metal? I see a paradox.
Man-made, yes. Even in different scenes however, the fundamental aspect of black metal was anti-Christianity. Varg has taken on various beliefs but all have been incongruent with Christianity. Not that his beliefs are even relevant, only the art that he puts out.
Only once aestheticists starting lapping up black and death metal did bands begin to use them as a vehicle for beliefs that completely contrast with their sound.