The problem isn't the GUEST prefix, which is there for a very good reason (to stop the situation where it was possible to post messages using someone else's name, thus sowing confusion. It seems that is how some people get their jollies.

But if two people or more sign in as GUEST, without adding a name, it becomes very difficult to respond to what they are saying. And that arouses the suspicion that they are doing this on purpose to make life difficulty for other people.

If people want to us a pseudonym, fair enough, it doesn't involve that kind of confusion. The only confusion is that, for example one "GUEST, gargoyle" might not be the same as the next "GUEST gargoyle". But that's life. (Incidentally, what good behaviour was that? I could put one of those emoticons in here, I suppose, but I can't think of one that's fitting.)