Read other letters about this article
I'm with you. Beyond the obvious examples (Stweart and Colbert), there are many "serious" liberals with fantastic senses of humor: Rachel Maddow, Keith Olbermann (yes, angry and blow-hardy, but also deliberately funny), Stephanie Miller. Writers as diverse as Studs Terkel, Garrison Keeler, Tina Fey, Dooce ...
Barack Obama has a fantastic sense of humor. So do both Clintons. Al Gore has a fun dry wit (despite the insistence that he's "boring"). I think Barney Franks is wickedly funny.
As you say, many in the GOP are "funny," but not intentionally so. (Rumsfeld comes closest, but, I'm not convinced he was in on many of his own jokes).
And conservative funny guys? What, Dennis Miller? Ann Coulter? (The best I can come up with is P.J. O'Rourke, and to be honest, I don't know how he reconciles his intelligence and temperment with his politics). Well, if that's your idea of "funny" then I can see why one would not understand "liberal humor."