I remember when USENET was largely civil, rational conversation. But then they let the AOLers in and it all went to heck. At least, we blamed the AOLers back then. I think what really happened was that as more and more people got Internet, it stopped being a bastion for engineers and scientists to talk engineering-y and scienc-y things.

I guess the point is, I find that any online channel dedicated to a particular purpose with a bent toward civil, rational conversation tends to find it.