It's a problem you run into with any darknet, but Freenet seems to have it a lot worse than Tor .onions. I have trawled around onionland a few times and saw only a few links that seemed like they might point in that direction, and didn't follow them. Most of Tor seemed pretty free of the stuff, and most of the directories seemed to have a policy against it.
I think this is a special case of a more general problem with libertarianism. There are in general two kinds of libertarians: those who want to maximize freedom for humanistic reasons, and those who want to maximize freedom because they want to be free to bully and exploit people without supervision or interference. Child pornographers fit into the latter, a category they share with people who want financial deregulation so they can fleece investors with pump and dump scams or KKK types who want the Federal government out of our lives so they can establish local tyrannies and oppress minorities.