The way I see it, this is a public Internet forum; I don't think that's been any sort of secret nor should it be a surprise, really. As soon as you post something in here, it's available to be viewed by pretty much anyone regardless of if they had a computer or not.
I've always tried to approach posting in these kinds of forums in the same manner as I conduct daily communication with other people -- electronic or otherwise. I try to maintain a consistency in tone, language, and viewpoints offered that's true to what I represent across all media.
I try my best to stand by everything I write here, on Aikido-L, and on other forums (fora?). I write as though my teacher(s) were reading what I was writing. I write as though my peers were reading. I write as though my mom were reading. And so on.
As such, I think it's important to realize that this is not a "private" means of communicating. As Bruce points out above, it can come and bite you on the rear. It can also bring you compliments and appreciation, too.
As Don points out, the manner in which you ressolve this issue ought to be no different than how you'd resolve a similar issue of offending someone in any other way.
Speaking one's mind is, of course, an extremely important part of one's life -- and something I value in my budo portion of my life as well. Many times, the hierarchical structure of dojo inhibits such. That's why I created these very forums and help maintain the Aikido-L mailing list; it's a way for people from all across the world to share their thoughts about aikido.
Yet, at the same time, I think there should also be a modicum of respect, etiquette, courtesy, and common sense too. Just because you're "speaking your mind" doesn't mean you're still not mindful about stepping on too many toes.
In any case, I hope everything gets resolved in a civil and constructive manner.
PS: If people have a very sensitive topic about which they want to post but wish to conceal their identity, the "Anonymous" forum was created for just that purpose. Please note, though, that forum wasn't created for people who wish to attack others, not bother to login/register, and such...