UPDATE: Chris says:

I think it's something to do with fearing that some people will take Carlin's word as 'a funny truth' rather than 'funny ridiculous' .... Ie, things will be a lot funnier if you knew that NOONE actually believed it to be truth... but knowing, or suspecting, that some people out there will actually think that's is true takes a LOT of the humour out of it.

Good point. You know, there's something to be said for comedy that doesn't attempt to divide or exclude or define loyalties. That's why Lewis Black's recent show seemed so much less fun than his earlier material—everybody can enjoy the "candy corn" routine; but once he starts playing to a particular audience, even if you agree with what he's saying, you can feel the vibe having suddenly narrowed. It's now about furtively giggling behind other people's backs; and that's just not as fun and fancy free.

Which is why I enjoy the redneck comics of the Blue Collar Comedy Tour so much: Larry the Cable Guy, Bill Engvall, Jeff Foxworthy, Ron White. It's all so positive. It's all jokes about being unsophisticated, being fat, being ugly, being dumb, being poor, being drunk—but it's all tongue-in-cheek. It's not mean-spirited. It's not critical. It's just fun. When I see someone like Ron White come on-screen with his drunken-master-storyteller face, I heave a sigh of gratitude—because you know what? It feels like Cosby. And that's about the highest praise I can think of.