"McGrath, can't a guest sign in as anybody? I mean, couldn't our flamer even sign in as me and start flaming/trolling? (If so, maybe I'd better join up, and fast, having given him/her the idea.)"

You've got it - so sign up pronto, if you can. Sometimes there are reasons people can't sign on as members, because their computers won''t allow it or something like that. But, apart from when thta is the case, I feel people who stick around and intentionally don't become members are acting a bit unfriendly. (For example any disagreement has to be conducted out in public - which is what helps turn things nasty sometimes.)