Having followed this forum for almost 8 years, I have always been impressed with the general level of civility, but I understand Jeff's concern as well.
I do not have time to follow that many, other than my own industry specific sites, so I can't comment on other forums.
I think our moderators do an excellent job, and are themselves models of articulate, civil communication.
My wife, a psychologist & therapist, would agree with Peter's comment, offering that these kinds forums can create a sense of intimacy that doesn't really exist, making it easier for someone to "go off" on another in a way they might not in person, given the relative safety of the environment.
She lost me when she went into those who through the internet find convenient ways to "discharge their psychopathologies...."
Myself, I prefer hand kneading.