To receive a pm, this nameless one must be a member hiding behind anonymity to attack someone else. I consider that to be far worse than a straightforward unidentified visitor.

I agree with you, Doug Chadwick. And if this site was members only, a member would have to use his/her name to post, and they might think twice before taking a pot shot when they know they will be known and made accountable for what they say. Although this step wouldn't get rid of all the nastiness, I think it would certainly lessen it.