I hate music

Fair enough, but even death and black metal are pretty diverse genres now. I understand why the screaming/growling vocals turn most off. In fact, they turned me off when I first got into the genre, but I liked the music well enough to continue listening, and over time I came to enjoy the vocals as well. A metalhead friend of mine once made an enlightening comment that helped me hear them in a new way when he said that growls/screams were basically just the vocal equivalent of a distorted electric guitar (as opposed to an acoustic guitar or clean electric guitar). I though that was a pretty interesting analogy and it helped me to hear the vocals more like a percussive instrument that just fit with the rest of the music. 

I also find it strange that people even describe those vocals as "devil-ish" or "demonic;" It's not like anyone has ever heard (or at least recorded) an actual demon/devil voice. All we have are movie depictions like in The Exorcist where the growls/screams are probably inspired by angry animals. 

I understand, but it's generally not wise to generalize about entire genres because there are almost always exceptions. That Stravinsky piece I linked to is certainly one of the most famous pieces from the 20th century that infamously caused a riot on its premiere (though that might've been due more to the ballet than the music).