I think you are actually being rather naive, how many parents really know what their teens are doing 24 hours a day.
My point exactly. If the parents refuse to except the responsibilty of raising their children then someone else will. The Government or Hollywood.
To answer your question quite a few. Because the parents are involved in their childs life, because they do accept that responsibility.
On the other hand I know many that have no clue what their children are doing or or when they are doing it.
Still we have a choice. Which group do we want to be in?
There is a choice because outside school and libaries kids can and still read and watch what they can get away with but why encourage it.
I see it as a moral responsibility for Christians to stand up for what is right not hide behind freedom of choice.