That's almost exactly what I was going to say. I certainly was in situations in college where I had to make my own choices, but by then I was mature enough and had a strong enough foundation to make the right ones. I didn't rebel or lack decision-making ability merely because my parents restricted the movies and shows I watched at 12 years old. On the other hand, the girls I knew who weren't being parented were the ones who got pregnant in h.s.
You can't shelter your children completely if they're going to school or otherwise spending any time away from you. But, you can set limits on what they watch and listen to when they are under your control and teach them what is right and wrong. It's frightening that some parents don't think it's their job to teach their children values and morals. That's the hardest and most important job of a parent, especially today when society wants us to believe consumption, desire, and personal choice are most important and there is no right and wrong.
I would be very upset with a parent who allowed her child to give a questionable cd to another child without checking with the child's parents. And I see nothing wrong with warning the parents and discretely throwing away the cd.