Everyone is prone to have a lapse of judgement and say something stupid. Cyril has thrown some stupid things in my direction. (I think we all have at some point)
For the most part, if you ask them to lay off, they will do so. Just be respectful. I can only hope that showing that kind of respect will be returned in kind.
One thing I try to get people to understand is that as soon as you start attacking the person rather than discussing the topic/idea, you're making yourself look foolish to the more intelligent people present. Also, returning such attacks makes you look equally foolish. If you feel the need to respond to such an attack, point out the attack, and indicate that you are willing to debate the merits of the topic/idea, but you're not going to engage in personal attacks. This obviously has random results, but it is the correct way to proceed.
I hate the idea of anyone feeling that they cannot post here. I have been in that situation before, and I have explained it to the others. I believe that the general consensus is that this community is made stronger through diversity rather than group think. Some of the best posts on here have gone against the grain of traditional thinking. Again, all I can ask is that people show respect towards one another, and debate the merits of the topic/idea rather than attack the person.