I think I just had a realization - the type where you suddenly make a connection between thoughts. The discussion above about "difference-ism" and the immigration "discussions", and the wealth gap, etc.
I think a major component of the sentiments many have in those areas is that microeconomics is zero sum, even though macroeconomics can be non-zero sum. So when people see anyone, especially of an "outside" tribe (be it color, creed, origin, whatever) enter their community they fear that instead of adding to the community, that "other" will instead displace an existing member of the community.
This is in fact rational to first-order observations: If you have a town that only has enough demand to hire 100 people, and another person comes in town, then either the new person doesn't get hired or one of the existing people gets replaced by the new one. This is almost always true, because a single new member of a community cannot - especially in the very short term - add enough demand to fully create an entire new job. But what about if the new person comes in and just starts a new business, providing competition? Let's say there were previously 2 suppliers of whatever the new person is selling, and the new one comes in. This means that the total demand for that good or service is now spread among 3 suppliers, not 2; all else equal, this means the two existing suppliers would have an immediate, significant reduction in business: instead of having 50% of the market, each would now only have 33% of the market. In a small market this is a huge effect.
What I have never seen is any kind of policy that addresses this kind of community impact. It gets washed away by the "big city" effect of mass media, and I don't think a lot of the discussion related to border towns addresses this. Maybe it does warrant federal assistance to border towns or something to mitigate this effect.