My advice, since this fellow is making you uncomfortable, would be to tell your facilitator about it. If this is a library group you find him at, then there really should be a librarian, or someone associated with the library there, at least occasionally. If it's not a library group, I guess you should use your social(spidy)-senses to find the most leader-like person in the circle, and ask them to talk to this chap in PRIVATE, unless you think you are up for it yourself.
I must stress that open and public confrontation is the worst possible thing to attempt. Although, I should also recommend that if you or anyone else does confront the guy, make sure someone else somewhere else knows when, where, why, and with whom this is happening. I don't mean to jump and shadows and blow me ol' whistle, but people who feature such topics so heavily in their writing, either have, have had, or want to have some sort of experience in the area featured. I'm not as familiar with the situation as you, but I should also suggest taking care in what ever course of action you settle upon, and not working alone.
This dude could need help, he might have been hurt once upon a time and is now trying to work through it all, he might be a threat to someone else, or any number of other possibilities. My last suggestion, rehearse or have your representative rehearse as many possible permutations of the situation as possible, and what recourses that are available. The worst thing you can do here is nothing, GD. Remember that.