Tabitha - how are films and books the same as a poster saying they raped a child? I'm not following your logic
I can't answer for Tabitha, but I see it as a poster telling a story. You don't know if it is true or not. You don't know if a story (a book, a film) is based on a true story, from the writers imagination, or from an act that the writer has committed.
I remember being horribly affected by a book (read whilst pregnant) where a baby was killed, carried around for years and eventually eaten. I mean, what sort of sick fuck thinks up stuff like that? The book was set in the past and in a war situation...maybe the author got the idea from stories he had been told about atrocities that had been committed? Or maybe it was something the author fantasised about doing? How do we know.
In the same way the author of that comment (about raping a child) could be military, or civilian. Could be making up a story or could be telling the truth. Could be telling his own story, or one that he has been told. Could be a frustrated wannabe trying to get 'in' with people he thinks are soldiers. Could be a MNer hoping to cause more controversy.
We don't know, and it's unlikely that the founders of ArRSe know either. The MODs probably don't know. Or maybe they do but think its funny to let him keep on posting.
We don't know anything
So ignore them. Ignore the site, ignore the threads, ignore the panty raids and invasions. If they are ignored they don't get any thrill out of what they are saying. By reacting and getting upset you are playing into their hands.
People like that are a bunch of nasty minded little pricks getting their rocks off on other people's upset. Don't give them the satisfaction.