It's interesting to see how little this kind of analysis seems to factor into the debate about immigration reform in the US.

Robert Putnam’s sobering new diversity research scares its author.

Putnam’s study reveals that immigration and diversity not only reduce social capital between ethnic groups, but also within the groups themselves. Trust, even for members of one’s own race, is lower, altruism and community cooperation rarer, friendships fewer. The problem isn’t ethnic conflict or troubled racial relations, but withdrawal and isolation. Putnam writes: “In colloquial language, people living in ethnically diverse settings appear to ‘hunker down’—that is, to pull in like a turtle.”

If he’s right, heavy immigration will inflict social deterioration for decades to come, harming immigrants as well as the native-born. Putnam is hopeful that eventually America will forge a new solidarity based on a “new, broader sense of we.” The problem is how to do that in an era of multiculturalism and disdain for assimilation.