Everything's been answered by Pin & harriergirl - "visitor messages" are a public system, like a blog. In the same way if one of you made your public profile something abusive, we'd edit it out - sure sure, it's "your" profile - but anything that's public, is public, and subject to forum rules. If you made your homepage be a link to a pornography site or warez site and we spotted in - bang, forum rules apply, "your" account or not. Hell technically PM's are also all subject to forum rules - there's no stipulation saying "If you want to be grossly abusive and horrible, feel free to PM somebody you don't like, it's none of the mods business because PM's are private and so you can do what you want!" but of course mods can't see PM's, so in this case it's up to the recipient to decide if it's abusive and report it, if they are upset by it.
I was absolutely flabberghasted by the topic, the nature of it, and the accompanying "Yeah those damned useless mods, deleting posts that breach forum rules which everyone can see.... grrrr, they're so useless, they should totally leave publically viewable flames and abuse!", that I didn't know whether to laugh or to cry.
One or two of the replies (pre-editing in particular) were priceless too, nice one guys
If ever there was an example of "Mods can't win", this is a prime one.
Thread of the day!