A long New York TImes op-ed summarizes the findings of the 2017 book The Space Between Us by political scientist Ryan Enos:
Enos then looked at results from 124,034 precincts, almost every precinct in the United States. Again:
“A white voter in the least-segregated metropolitan area was 10 percentage points more likely to vote for Obama than a white voter in the most-segregated area.”…
These voting patterns, according to Enos, reflect what might be called a self-reinforcing cycle of prejudice.
“Prejudice may have helped cause segregation, but then the segregation helped cause even more prejudice.”
In other words, it is not just problematic that people of different racial/ethnic groups and social classes choose to (possible more often for whites and those with more financial resources) or are pushed to live in different places from each other. The residential segregation then has a feedback loop where those differences reinforced by spatial arrangements are perpetuated and perhaps even amplified.
As more of the op-ed explains, simply putting people together (such as suggested by Allport’s contact hypothesis or in the train experiment described in the essay) is not a silver bullet for forging relationships, networks, and reduced prejudices. Even as attitudes toward other groups have improved over time, what would push wealthier whites to sacrifice or put themselves into uncomfortable positions when they do not have to?