This is an old and tired debate that has been waged against every new style of music to EVER come out. In the 20's: Jazz was the devil's music that led sweet and innocent children to commit sins of the flesh. In the 40's and 50's: Rock-n-Roll was the devil's music that led sweet and innocent children to use drugs and commit sins of the flesh. And now, Rap and Metal are the devil's music that lead sweet and innocent children to use drugs, steal, murder, and commit sins of the flesh. It's all built out of this disconnect that has been rising between parents and their children because of the independent nature of the world today. (This is all a theory I've been working on for a few years now, but it fits the discussion so I decided to answer with it.)

Also, if you're going to use the genre's rap and metal you have to dissect them. There are several different kinds of rap and several different kinds of metal, not all are bad, not all are good. I personally have more personal knowledge and experience with metal so I'll talk about that one. There are Christian Metal bands, believe it or not. I've seen a few perform, and honestly, it's hilarious. Then there are those like Death Clock that are more of a Death Metal. They have much darker subject matter.

Either way, I don't think anything has to do with the music or the lyrics. Kids aren't stupid. They understand that there is a difference between song lyrics and reality. They don't go out and shoot someone because the music they listen to told them to. People are simply using the music as a scapegoat for their kids behavior.