Young kids shouldn't be allowed to listen to music advocating violence until they are mature enough to handle it. When they reach a certain age, they should be allowed to make their own decisions about what they listen to. If they are exposed too early, they might be negatively influenced by it.
Advocating violence is not the purpose of music television. Just as the movies are inundated with violence, people have a choice to pay for the movie or to not watch the movie. The television is a platform that can control the violence and be an advocate of such violent action.
I think that music should be able to advocate anything that it wants. It is freedom of speech. People have a right to say what they want. I think that stores can choose to sell or not sell music that advocates violence. Also I think that individual people can choose whether or not to listen to music advocating violence.