First off, a commentary by Rick Perlstein about the long history of incivility. It apparently has roots in conservativism, although I suspect liberals have their own cadre of wingnuts.
Regarding health care reform; it is becoming clear that Lyndon Larouche's PAC is behind the Nazi meme. The epitome of this is the Barney Frank putdown of a Larouche supporter, Obama/Hitler picture in hand. She makes a point of saying that Larouche has defeated the proposed policy, something the MSM failed to notice. Over at Factnet the Larouche forum has been getting quite a workout, courtesy of a poster named xlcr who has been busy scooping up articles from around the Internet about the Larouche connection. The legitimate conservatives have been busy trying to keep their distance from Larouche's lunacy, trying to pin it on the Democrats, who officially refuse to have anything to do with him.
I suppose the message here is that change begets the crazy, which begets the wingnuts, which begets incivility, and those of us with genuine concerns need to ensure we don't find the wingnuts velcroed to us or we'll never get heard.