As a general principle, I support moderators using their discretion to manage the tone of forum discussions, particularly in the context of personal attacks. In principle, I support moderators taking actions up to and including nuking of topics and permanently banning members.
I have to say that I do too. For one, definitely not every single post is going to be appropriate for the site. I posted something that I thought was funny but contained a lot of foul language (an external link) and was politely asked by a moderator to edit it out, which I did. In hindsight, I thought this was a completely appropriate thing for the moderator to do and I was like, what was I thinking anyway...
As everyone knows, I run a very active online community too. I went through this same issue early on and before anyone could make a posting asking what the policy was, I wrote one up myself explaining what the mission and purpose of my site was, what was appropriate content, what was inappropriate content, and what could actually get you restricted from using the site. It has been very helpful in setting expectations for site users.
My site, unlike KF, uses a true relational database for fully threaded discussions so when an inappropriate message does appear, it can be deleted without affecting the rest of a thread. Also, I am the owner of the site and its only moderator which makes it clear that all blame for deleted content lies solely with me. I make it very clear in the footer on every bulletin board page that the site is most definitely not a free for all site - NOT everything goes. I'm not expecting that everything goes here either.
-Scott