Even Michael Moore, the most noxious liberal windbag with any sort of actual media platform from which to reach people, is nothing compared to the sort of hatred spewed on a regular basis by the masses of right wing commentators.
Hell, even that idiot with his "little eichmans" crap wasn't being half as nasty as Michelle Malkin on a good day.
Also, and this may just be my bias showing, I find the targets of leftists hate -- the rich, powerful and elitist who dehumanize those whose shouders they ride on -- much less sympathetic than the targets of right wing hate: the poor, the disenfranchised, minorities, gays, women, immigrants, etc. That alone makes right wing hate seem infinitely nastier.