I didn't know about Nifty until this thread was posted. I just skimmed through four stories and didn't see anything about adults molesting prepubescent children (which I presume exist as per the comments in this thread). I did however see stories about pubescent minors involved in sexual relations, which would indicate hebephilia and ephebophilia, and not necessarily pedophila.
Should they be banned? I don't know the answer to that. Thought-policing and regulating free speech are on a slippery slope. I agree with banning literature that incites hatred so I guess it's perfectly consistent with my views that we also ban literature that incites child abuse. But do stories involving minors necessarily do that? I have some serious doubts. If perverts are going to get off I'd rather them do it with make-belief minors and not real minors. Of course, we'd rather them not get off at all, but that's impossible to enforce. Even if they don't put their fantasies on paper, they still have them in their head.
I notice that society has a double-standard with violence. Murder is worse than rape and child molestation, yet murder is depicted in so many books, TV shows, video games, and movies, I can't even keep count. The other day I asked my friend's chatty little eight-year-old son what he wanted to be when he grows up and he told me he wants to be a gun tester, then went on a tirade about all the different weapons he could develop to kill people, particularly a rifle with a sword on the end that you could also stab people with, and proceeded to act out the different scenarios and places on the body where such an attack could occur. (He even mentioned how much easier it would be to kill senior citizens because they're frail!) All I asked him is what he wanted to be when he grows up. It seems he's been playing too many violent video games (he mentioned Halo) and violent movies (he mentioned zombie movies.)
If we are to accept the argument that such depictions don't incite violence, we must also accept the argument that such pervy stories don't incite perversion. I'm thinking maybe people's disgust for pedophilia and the normalization of violence has a lot to do this double-standard. Again, I don't know the solution to this, but it's food for thought.