There's a post at www.bycommonconsent.com that I found quite interesting.
The sister missionary in our MTC district (who ended up going to the same mission as I did) was also of the opinion that rock music was of the devil. Interestingly enough, she was also the most troubled missionary I ever met. I have a great respect for my MTC missionary companion, the only other missionary from that MTC district who went to our mission. Why? I never once heard anyone tell horror stories about this particular sister in the MTC--and believe me, there were stories to tell. In other words, he had great gossip to share, and he kept his mouth shut.
I did hear some about how she was in the mission, and it was bad (although not as bad as the MTC stuff...)
Anyway, my point is...rock music (even some hard rock or metal) can be good, and even uplifting and inspiring, and those who deny this (besides sometimes having deep psychological problems) may be a contributing factor at driving people away from the church.
I consider myself lucky to have good role-models inside the church who still love rock music (thanks Dad).