[WS:] This was my impression as FOB too. But then I realized it is more about a combination of geography and work schedule than anything else. Back in Europe, people would socialize after work, going to a pub or someone's flat to hang out. It was possible because they lived closer to each other and did not have to drive. They might have had a few beers and the go home by bus. Here, everything is sprawled so people have to drive to work, In fact, over 86% of people drive http://www.census.gov/prod/2011pubs/acs-15.pdf. So that kills socializing - you cannot go to a pub near you place of work because you have to drive, and once you get to your bedroom community it is already to late to go out.
What is more, since people move from one bedroom community to another chasing after jobs, they do not develop the same neighborhood relations as those who do. They are more likely not to know their neighbors beyond the conventional "hi" on weekends.
This also explains the popularity of religion in the US. Church going is one of the few socializing venues available in suburban America - and people who go to church often do so for social rather than religious reasons. I often observed that church goers almost never talk about religious subjects (e.g. faith, doctrine, theology, etc.) when talking about their church experiences - they almost always talk about their social experiences: who was there, who did what, who is in cahoots with whom etc.
I would say that two things that poison socialization in the US are automobile and suburbia. Social life seems to thrive in urban environments where people actually live and work in the city and are not as dependent on cars. So while US suburbia are social graveyards comparing to Europe and Latin America, US cities are as lively, and sometimes even more so than European or Latin American cities. As and interesting point - the Amish rejected automobile precisely for that reason, they feared it would kill their community.
As to your observation about ethnic prejudice - it is universal. In every part of the world I visited, and I have been to some 40 or so countries, I have seen people holding prejudices about other ethnic groups. It is a part of the human nature - or more specifically, a product of what Kahneman calls "fast thinking" (i.e. making judgments based on stereotypes http://en.wikipedia.org/wiki/Thinking,_Fast_and_Slow). So you are bound to see it when there is interaction among different groups. It becomes problematic only when it is not controlled by what Kahneman calls "slow" or rational thinking i.e. when it is flamed by demagogues or institutionalized. Again, US suburbia and car-based transportation tend to increase segregation and help keeping the ethnic prejudices alive.
-- Wojtek
"An anarchist is a neoliberal without money."