It's as much about jealousy in the asexual or unattractive. Strange and annoying motives, but the protection of kids is certainly not one of them.
Interesting point. My experience says that you are right.
I cannot figure out why knee-jerk libertarians think they have the right to walk into an environment and cr@p on the floor, and if everyone else doesn't like it, they should leave. There's also the premise of respecting other people's sensibilities. If somebody wants to look at porn, they should get their own d@mned computer and internet connection.