It's pointless arguing with an anonymous GUEST by citing quotes, because there's no way of knowing if the quotes come from the same GUEST or not.

And no good trying to make sense of the personality quirk involved, or pointing out that adding a pseudonym to GUEST in no way infringes their total anonymity, but merely helps avoid people getting at cross purposes, and it makes it much more convenient for other people. When someone isn't listening they aren't listening.

The best policy is to totally ignore them, and hope they'll either slope off, or preferably in some cases (and in spite of what some people have said, I'd say this is one of them) the GUEST will just quietly add on a pseudonym and keep posting, and probably we'll never know.