I don't know exactly when the conventional wisdom changed to create all-conservative talk stations and all-liberal talk stations, but that's the way things are now, for the most part. Maybe it's a sign of the increasing polarization of American political discourse. Or maybe PDs just got tired of hearing complaints from one host's fans about the other host's show. It's kind of a shame, actually. I was talking about this with a host who lands on the liberal end of the political spectrum who's worked at some conservative stations. And the reaction he got as a left-winger on a right-wing...