By many accounts, Keith Olbermann’s abrupt exit from MSNBC was a human-resources move, not an ideological one; his mercurial personality has seldom served him well in the workplace. But people of all political stripes should see his departure as a chance to change the tenor of the national conversation.It was Olbermann whose increasingly partisan rants helped transform MSNBC from a neutral news channel to a left-wing counterpart to the Fox News Channel. The move was good for MSNBC’s..