There are reasons homogeneous communities form in the U.S. A few of those reasons have to do with city planning and legislation. City planning can be racist in nature and promote exclusionary communities. Redlining, while not typically state legislation, is a good example of practices that contributed to the formation of primarily white communities.
You mention people making distinctions based on where you go to work, where your kids go to school, what kind of car you drive, how you dress, etc.. If I'm black and couldn't afford college for various reasons, I'm going to have a hard time getting a job that would allow me to buy the kind of car, dress in the clothes, send my kid to the schools, buy a house where the other people who had a _systematically_ easier go at life would.
My point is; When people think of those who are in and outside of their community there is latent racism. Why can't we treat people from outside our community as the same as people inside? If we better understand and critique what a community is and how it forms I think it's possible.