What emotional and mental harm are you talking about, Rhapsody? How does the user take out this harm you speak of on his wife, lover, child, etc. (if he has them)? Again, I'm not saying he isn't sick, but I don't believe in condemning someone for thoughts and fantasies.

As for science showing harm, science is not one entity. There are those in science who do studies on all kinds of things and get one result, whereas others in the same field get different results. People get harmed by knives. Shall we make knives illegal? It wouldn't do any good. Those who want to get knives (or porn), will. You act as though making a law is going to stop people from buying or getting porn, guns, etc., and that just isn't so. They can't even get gangbangers off the street, unless they catch or are called for them doing something illegal, or they have warrants for such people.