I actually had this argument quite a few times with a lot of folks over on the Black Sabbath website... I would even explain in detail that they are necessary, when one is trying to look for bands with a specific aesthetic or sound... I mean, what's easier to do a search for... "black metal", or "metal that generally contains high-pitched, tremolo-picked melodies, occasionally lo-fi production, and shrieked vocals"?
But as usual, I'd get the same meatheaded, unsubstantiated response that they had given at the beginning of the argument: "it's all just music man, the only genres are 'music I like' and 'music I don't', fuck labels, derp", which drives me fucking mad.