Michelle Malkin has done a superb job of documenting the left wing nuttery over the past decade. S.E. Cupp has a similar article, as does PJM. The true vitriol and eliminationist rhetoric of the left has no analog on the conservative right. The right wants to argue policy; the left wants to delegitimize their political opposition so that they don't have to address their policies.
Trying to explain the acts of the left in response to the Arizona mass murder, George Will makes my point much more eloquently:
A characteristic of many contemporary minds is susceptibility to the superstition that all behavior can be traced to some diagnosable frame of mind that is a product of promptings from the social environment. From which flows a political doctrine: Given clever social engineering, society and people can be perfected. This supposedly is the path to progress. It actually is the crux of progressivism. And it is why there is a reflex to blame conservatives first. . . .
Let us hope that Dean is the last gasp of the generation of liberals whose default position in any argument is to indict opponents as racists. This McCarthyism of the left - devoid of intellectual content, unsupported by data - is a mental tic, not an idea but a tactic for avoiding engagement with ideas. It expresses limitless contempt for the American people, who have reciprocated by reducing liberalism to its current characteristics of electoral weakness and bad sociology.
Update: James Taranto made the following observation on the left's treatment of political violence, penned in light of the left's outrageous defense of Frances Fox Piven's calls for Greece-like riots in America:
America's liberal left is preoccupied with salacious fantasies of political violence. These take two forms: dreams of leftist insurrection, and nightmares of reactionary bloodshed. The "mainstream" media ignore or suppress the former type of fantasy and treat the latter as if it reflected reality. This produces a distorted narrative that further feeds the left's fantasies and disserves those who expect the media to provide truthful information. . .
In other related news, both the New York Times and Michael Tomasky have demonstrated despicable hypocrisy, penning articles now tying the murders in Arizona to the right with not a shred of evidence, yet in response to the Ft. Hood shooting, with evidence piling up left and right about the shooters motives, counciled caution and refused to draw conclusions.
The most sane response to this mass murder has come from the people most injured by it - the parents of Christina Taylor Green, who have described the monstrous event that claimed the life of their child is "the cost of living in a free society."
And lastly, this from Instapundit:
As I think about it, the mental process seems to be something like this:
Lefty: Sarah Palin and the Tea Party movement encourage hatred and violence!
Questioner: How do you know?
Lefty: Because whenever I think about them, I’m filled with hate and a desire to do harm!