http://www.theamericanconservative.com/articles/fragmented-future/

In the presence of [ethnic] diversity, we hunker down. We act like turtles. The effect of diversity is worse than had been imagined. And it’s not just that we don’t trust people who are not like us. In diverse communities, we don’t trust people who do look like us.
—Harvard professor Robert D. Putnam
It was one of the more irony-laden incidents in the history of celebrity social scientists. While in Sweden to receive a $50,000 academic prize as political science professor of the year, Harvard’s Robert D. Putnam, a former Carter administration official who made his reputation writing about the decline of social trust in America in his bestseller Bowling Alone, confessed to Financial Times columnist John Lloyd that his latest research discovery—that ethnic diversity decreases trust and co-operation in communities—was so explosive that for the last half decade he hadn’t dared announce it “until he could develop proposals to compensate for the negative effects of diversity, saying it ‘would have been irresponsible to publish without that.’”
In a column headlined “Harvard study paints bleak picture of ethnic diversity,” Lloyd summarized the results of the largest study ever of “civic engagement,” a survey of 26,200 people in 40 American communities:
When the data were adjusted for class, income and other factors, they showed that the more people of different races lived in the same community, the greater the loss of trust. ‘They don’t trust the local mayor, they don’t trust the local paper, they don’t trust other people and they don’t trust institutions,’ said Prof Putnam. ‘The only thing there’s more of is protest marches and TV watching.’
Lloyd noted, “Prof Putnam found trust was lowest in Los Angeles, ‘the most diverse human habitation in human history...’”
Before Putnam hid his study away, his research had appeared on March 1, 2001 in a Los Angeles Times article entitled “Love Thy Neighbor? Not in L.A.” Reporter Peter Y. Hong recounted, “Those who live in more homogeneous places, such as New Hampshire, Montana or Lewiston, Maine, do more with friends and are more involved in community affairs or politics than residents of more cosmopolitan areas, the study said.”
Putnam’s discovery is hardly shocking to anyone who has tried to organize a civic betterment project in a multi-ethnic neighborhood. My wife and I lived for 12 years in Chicago’s Uptown district, which claims to be the most diverse two square miles in America, with about 100 different languages being spoken. She helped launch a neighborhood drive to repair the dilapidated playlot across the street. To get Mayor Daley’s administration to chip in, we needed to raise matching funds and sign up volunteer laborers.
This kind of Robert D. Putnam-endorsed good citizenship proved difficult in Uptown, however, precisely because of its remarkable diversity. The most obvious stumbling block was that it’s hard to talk neighbors into donating money or time if they don’t speak the same language as you. Then there’s the fundamental difficulty of making multiculturalism work—namely, multiple cultures. Getting Koreans, Russians, Mexicans, Nigerians, and Assyrians (Christian Iraqis) to agree on how to landscape a park is harder than fostering consensus among people who all grew up with the same mental picture of what a park should look like. For example, Russian women like to sunbathe. But most of the immigrant ladies from more southerly countries stick to the shade, since their cultures discriminate in favor of fairer-skinned women. So do you plant a lot of shade trees or not?
The high crime rate didn’t help either. The affluent South Vietnamese merchants from the nearby Little Saigon district showed scant enthusiasm for sending their small children to play in a park that would also be used by large black kids from the local public-housing project.
Exotic inter-immigrant hatreds also got in the way. The Eritreans and Ethiopians are both slender, elegant-looking brown people with thin Arab noses, who appear identical to undiscerning American eyes. But their compatriots in the Horn of Africa were fighting a vicious war.
Finally, most of the immigrants, with the possible exception of the Eritreans, came from countries where only a chump would trust neighbors he wasn’t related to, much less count on the government for an even break. If the South Vietnamese, for example, had been less clannish and more ready to sacrifice for the national good in 1964-75, they wouldn’t be so proficient at running family-owned restaurants on Argyle Street today. But they might still have their own country.
In the end, boring old middle-class, English-speaking, native-born Americans (mostly white, but with some black-white couples) did the bulk of the work. When the ordeal of organizing was over, everybody seemed to give up on trying to bring Uptown together for civic improvement for the rest of the decade.

There's a lot more to chew on in the article.  RTWT.