Today I finished reading Charles Murray's 2012 book Coming Apart: The State of White America, 1960-2010. In the book, Murray notes what others have found: that diversity undermines community formation. The worry is that a nation as diverse as America will have a hard time re-forming (i.e.: forming again) a cohesive social core.
I think it's true that society cannot be based on diversity, but I also think you can have a diverse society if some OTHER common factor exists. For example, when the common trait was support of the American experiment, we were able to take millions of ethnically- and linguistically-diverse people and form a society. You don't look like me or talk like me or worship God like me, but you value personal freedom and personal responsibility, and so do I, so we will work together to support those values.
What about now, when most of the people who are coming to America couldn't care less about ideology, and they are drawn by either economic or safety concerns? Can we base a society on "we both want to get as rich as possible"? Murray writes about what Edward Banfield called "amoral familism," which is basically the plot of the entire Fast and Furious franchise: nothing matters but family. I would argue that the current view of America, as the place you can get richest, is an amoral familism base on which society cannot be built. There has to be something common about the product, not just the motivation. Knowing you're out to get yours, just like I'm out to get mine, doesn't engender trust. It probably undermines it, actually. Just look at all the reality-TV figures who "didn't come here to make friends."
What is the likelihood that we can get a third of a billion people to agree on some underlying principles? I think the size of the American political entity undermines the commonality necessary for societal formation or preservation. Not in the sense that there should be 50 sovereign states, but in the sense that there should be 500 of them. A thousand. Basically a collection of city-states. Within the city-state, there's the homogeneity necessary for community. Outside the city-state, the required homogeneous elements become just the bare minimum required for the type of public goods that would have to be provided by a federal government. Could we get 1,000 city-states to agree on deterring a North Korean military threat? I think so. Can we get them to agree on a third-grade curriculum? Why do we need to?
Ultimately, I think we will get the re-creation (i.e.: creating again) of social capital when we stop celebrating diversity qua diversity and start looking for commonality. Is there common ground between a rural religious conservative and an urban transgendered atheist? Sure: they both want to be left alone to do their own thing. That would be one of the handful of bedrock principles the entire federation of city-states could support. The more community we want, the smaller the polity needs to be. Like Hayek said, Bermuda could implement socialism without compulsive methods, but anything much larger than that cannot. Paradoxically, we'd get stronger support of America's core principles if we stopped trying to impose a political system that requires homogeneity onto a heterogeneous society as large as America.