One reason commercial liberal talk radio’s never quite succeeded is that NPR is a network with liberal hosts, liberal guests, and liberal callers. This perfect storm of unanimity displayed itself on Thursday’s Diane Rehm Show, when they discussed the push for more gun control. There were no guests from the NRA, just moderate Richard Feldman, who wrote a book about his “confessions of a gun lobbyist.” On the other hand, Rehm brought on Mark Kelly, the astronaut husband of disabled ex-Rep. Gabrielle Giffords to talk up his new gun-control group, as well as an anti-gun New York Times reporter and...