OK, it's a controversial question, I am not trying to be Tippa Gore here, but an interesting one; why so much obsession with dead babies, blood baths, carnal corpses and devils
For a death metal fan my next statement (I only like it for the riffs) is like saying "I only read Playboy for the articles".
But you can ask "why do all the loonies have all the good guitar work" when it comes to metal.
Another way of looking at it is the dark themes are a healthy release; I know Henry Rollins helped me alot (his poems are pretty catharctic)
Image: Courtesy Century/Quarterstick