Certain people (and I'm looking at you, Todd Zywicki, although not only you...) have been arguing that there is a lamentable lack of diversity in academia, because when you lay all the professors end to end, most of them are registered Democrats.
On the surface there seems to be something to the concern. Very little knowledge exists in absolute terms. Its instruction always comes couched in some perspective. Diversity in academia is important in order to make sure that students can learn information from a variety of viewpoints. Without it students are susceptible to learning dogma in place of insight. With a diversity of viewpoints, however, students can figure out which parts of the package are subjective and which are objective (to the extent that anything is) and be exposed to more knowledge than a single worldview would be able to impart. Moreover, being exposed to different ways of thinking will result in their own becoming all the more sophisticated.
There is more than can be said in support of academic diversity, but the problem addressed here is that political diversity does not map to academic diversity. The subtext to the argument that there should be more Republican professors is that the world can be cleanly divided into these two viewpoints, and therefore the academic positions should be doled out equitably between them. Such a belief is a fallacy.
For one thing, it presumes that Democrats and Republicans are opposite sides of the same coin. They're not. They are really apples and oranges. They are not two antithetical viewpoints on the same subject, where one wants black and the other white. In reality, one wants black and the other wants doorknob. Politically, the doorknob faction may express the preference by advocating for white, but what it really wants is something entirely different. It's just that the polical forum reduces its expression to a specific manifestation of preference, but one that may have little to do with what it actually wants in the picture.
Furthermore it's not clear exactly what the party preference serves as a proxy for. It supposes too much to presume that all Democrats are Democrats for the same reason, or that all Republicans are in firm agreement about what it means to be Republicans. As varying ideology get distilled into political pragmatism, you may often get strange bedfellows. Afterall, in the US there are really only two choices. It's therefore unsound to believe that isn't a tremendous variance among people who might happen to identify politically under the same label.
But to the extent that Democrats differ from Republicans - that liberals differ from conservatives - I don't think it would necessarily be a bad thing to have more liberals. They aren't equal viewpoints. Conservatives, by definition, generally tend to see the world very precisely. They have it all worked out, and don't like it when people vary. Liberalism, on the other hand, by *its* very definition implies openmindedness. There's room in liberal ideology for conservative preferences, but it's not preclusive of other ones. I don't think, however, that the same can be said in the reverse.
For an excellent essay addressing the futility of the Conservatives' argument, I recommend Aaron Swartz's "Intellectual Diversity at Stanford." For the humor-impaired (judging by the comments on his site there are clearly quite a few out there) his piece is satire, of the Jonathon Swift tradition.