Two things to keep in mind: if your son realizes you're trying to wean him off his awful music, he'll close up completely to any suggestions you might have. If you forbid him to listen to certain music based on lyrical content or imagery, he'll get a taste for forbidden fruit and move on to deemedly less appropriate tunes.
My parents made the mistake of trying to cut off my hard rock intake, and I ended up with Carcass and Dead Infection albums in a steady rotation
