Following up on this post, note Clive Crook’s comments. The Nozick quote is rather apt, though of course, bias is reinforcing–conservatives don’t go into academia in large part because they are convinced that thanks to the massive disparity in numbers between liberals and conservatives, the life of the conservative academic will be a lonely and besieged one. As a consequence, the disparity grows still more massive, which only serves to reinforce conservative skittishness about entering academia, which causes the disparity to grow still more massive . . . etc.
As for Paul Krugman’s thoughts on the matter, they should be of little consequence. Krugman thinks that all of his ideological opponents are stupid and venal. One cannot turn to him for dispassionate analysis on this kind of issue.