Daniel Henninger explores "The Death of Diversity" as an ideology:

Now comes word that diversity as an ideology may be dead, or not worth saving. Robert Putnam, the Harvard don who in the controversial bestseller "Bowling Alone" announced the decline of communal-mindedness amid the rise of home-alone couch potatoes, has completed a mammoth study of the effects of ethnic diversity on communities. His researchers did 30,000 interviews in 41 U.S. communities. Short version: People in ethnically diverse settings don't want to have much of anything to do with each other. "Social capital" erodes. Diversity has a downside.

Prof. Putnam isn't exactly hiding these volatile conclusions, though he did introduce them in a journal called Scandinavian Political Studies. A great believer in the efficacy of what social scientists call "reciprocity," he wasn't happy with what he found but didn't mince words describing the results:

"Inhabitants of diverse communities tend to withdraw from collective life, to distrust their neighbors, regardless of the color of their skin, to withdraw even from close friends, to expect the worst from their community and its leaders, to volunteer less, give less to charity and work on community projects less often, to register to vote less, to agitate for social reform more, but have less faith that they can actually make a difference, and to huddle unhappily in front of the television." The diversity nightmare gets worse: They have little confidence in the "local news media." This after all we've done for them.

Colleagues and diversity advocates, disturbed at what was emerging from the study, suggested alternative explanations. Prof. Putnam and his team re-ran the data every which way from Sunday and the result was always the same: Diverse communities may be yeasty and even creative, but trust, altruism and community cooperation fall. He calls it "hunkering down."

Related: Patrick Hynes suggests that "American conservatism has devolved from a movement into an identity group."