Even if only twenty percent of American college professors lean to the right, that still means that intellectual diversity on campus exceeds racial—and, in some disciplines, even gender—diversity by a significant margin. Since the groups that decry ideological imbalance (ACTA, NAS, etc.) are also fiercely opposed to affirmative action, it might be worth asking them to address this point. If, as they believe, the persistence of an overwhelmingly white, male professoriate is not prima facie evidence of racial discrimination, then why can't we assume that the numerical dominance of liberals is similarly benign?
Maybe conservative intellectuals just aren't trying hard enough.