Some of them have taken on the responsibility of prosecuting vendors for selling certain material to minors. It's not what the child is doing; it's what the vendor is doing.

I'm not sure I agree. If the parents don't do it, someone ought to. I disagree on the part that all types of porn (especially by the USA level of prudishness) is necessarily harmful to 16-year-olds.

I believe that too... but you and I are very solidly in the minority.