Diversity is widely celebrated in American society. But from a social psychological point of view, diversity ought to cause a number of problems, such as divisiveness and conflict. A resolution of this paradox is proposed: There are several kinds of diversity, with different profiles of costs and benefits. In particular, moral diversity is identified as being problematic and even self-contradictory. Three studies of attitudes and desires for interaction among college students confirmed that moral diversity reduces desires for interaction more than does demographic diversity, and that both kinds of diversity are valued more in a classroom than in other social settings. These findings have important implications for discussions of diversity, multiculturalism, affirmative action, identity politics, and immigration policy.