I think that people who complain about the "inauthenticity" (poor word choice... authentically or inauthentically what?) of death metal and black metal vocal stylistics are probably suffering from a fixation on traditional, conservatory oriented musical techniques. And really missing the point.
I generally reject most "sung" vocals in metal because I think it distorts the message of the music. Rasped, roared, or similarly 'distorted' vocals communicate one thing; "clean" vocals communicate an other. In the context of music that communicates a daemonic or feral power, daemonic and feral vocalizations seem more appropriate.
Keep in mind, the best death metal and black metal vocalizations are not merely angry shouting. It is a highly controlled sound, and should be regarded as an actual form of instrumentation, so to speak...
And by the way, it is easy to perform metal vocalizations without annihilating your voice. Especially in death metal, the sound is not abrasive to the throat. That's my experience, anyway.