Do you think prohibiting porn would be any more effective? Especially considering that porn doesn't have to be smuggled over the border- it can simply be downloaded from a Swedish, Dutch or Russian company.
I assume you've been reading on this thread that just about all porn is legal anyways, so why the question?
The problem is that we're not prohibiting porn. Or, more precisely, we're prohibiting porn the same way we prohibited alcohol -- instead of speakeasies we have adult bookstores. Wink wink, nudge nudge.