jeanne d'arc (as usual) gets it
Body and Soul has a great piece on why there isn't a leftist Ann Coulter.
Leftist politics has its roots in compassion; we'll never be comfortable or convincing selling meanness and hatred. More than that, I think in the long run, nastiness is counter-productive. Ann Coulter's political pornography may feed the lusty anger of bigots and gun nuts, but I doubt she's ever lured a single person off the fence. She's a whore, not a siren. There may be some value for the right in holding the interest of its angry, resentful base, but the left's base isn't angry or resentful. It's frustrated and ready for change, but it isn't inherently angry. It isn't entertained by hostility. And that leaves very little for a left-wing Coulter to feed on.