When I'm talking to people from outside Washington, one question inevitably comes up: Why is the media so liberal? The question often reflects a suspicion that members of the press get together and decide on a story line that favors liberals and Democrats and denigrates conservatives and Republicans.

My response has usually been to say, yes, there's liberal bias in the media, but there's no conspiracy. The liberal tilt is an accident of nature. The media disproportionately attracts people from a liberal arts background who...