I asked Douglas Massey, a professor of sociology and public policy at Princeton, about the difficulties facing proponents of increased integration.

Massey, who has written that “residential segregation constitutes the ‘structural linchpin’ of racial stratification in the United States,” described to me in an email the way in which his research suggests segregation can reinforce itself:

Research shows that whites substantially overestimate crime rates in communities that contain blacks, and that even controlling for crime rates, school quality, and home values, whites grow progressively less likely to purchase a home in a neighborhood as the percentage of blacks rises. These sentiments both cause, and are caused by, segregation as both conscious and unconscious racism structures the social cognition of Americans, and because basic institutions such as criminal justice, real estate, land use regulation, banking, insurance, and labor markets are highly racialized.

Once a large black population is highly segregated in an urban setting, Massey continued, “it becomes very difficult to move toward integration because segregation perpetuates the neighborhood conditions that sustain the negative stereotypes.”

Housing segregation, according to Massey’s analysis,

ultimately derives from the persistence of anti-black racism and the more recent rise in anti-Hispanic prejudice. These sentiments are bound up with persistent negative stereotypes about crime, sexuality, and intelligence.

Most whites, Massey wrote,

no longer support segregation as a matter of principle, but they are still made uneasy by the presence of very many blacks (and to a lesser degree Hispanics) in practice, especially in intimate settings such as neighborhoods, schools and families.

There are examples of successfully integrated communities, but they are the exception rather than the rule, Massey said:

Places with small, affluent black populations have been able to integrate, but the nation’s largest black urban communities remain stubbornly stuck at high levels of segregation, and about a third of all urban blacks live under conditions of hyper-segregation.

Scholars are continuing to make an effort to understand the motivations of white Americans.

Ann Owens, a sociologist at the University of Southern California who has written extensively on the subjects of race, income and neighborhoods, replied to my inquiry:

I think separating out racism from fears of losing advantages is difficult. Many parents voice support for integration in the abstract, but then of course we see protests and pushback when their own child, or other stakes, like property values, might be affected. Few parents articulate that school racial composition is what they make schooling decisions on, but studies show that once you control for all the other things parents might say race is a proxy for — class, test scores, resources, etc. — white parents still prefer schools serving fewer black or Hispanic kids.

In a 2013 paper, “Race and neighborhoods in the 21st century: What does segregation mean today?” Jorge De la Roca, of the University of Southern California, Ingrid Gould Ellen and Katherine M. O’Regan, both at N.Y.U., determined that

the neighborhood environments of minorities continue to be highly unequal to those enjoyed by whites. Blacks and Hispanics continue to live among more disadvantaged neighbors, to have access to lower performing schools, and to be exposed to more violent crime.

These differences, in turn, reinforce both the race prejudice and the stereotypes that drive many whites to oppose government action to achieve integration.

Take neighborhood school proficiency ratings. De la Roca, Ellen and O’Regan found that the average white person lives in a census tract where the nearest elementary school ranks at the 58th percentile in proficiency while the nearest school to the average black person ranks in 37th percentile, “resulting in a 21 percentage point racial gap in proficiency ranking.”

Or take crime. De la Roca, Ellen and O’Regan write that the average white person lives in a census tract “with a violent crime rate at the 37th percentile in their city” while the average black person lives in a tract at the 66th percentile. For poor whites, the nearest elementary school has a 50 percent proficiency rating compared with 30.1 percent for poor blacks. The violent crime level in poor white census tracts is in the 55.5th percentile compared with the 74.5 percentile in poor black tracts.

Sean F. Reardon and Joseph Townsend, both of Stanford, and Lindsay Fox, a researcher at Mathematica Policy Research, reached similar conclusions in their 2017 paper, “A Continuous Measure of the Joint Distribution of Race and Income Among Neighborhoods.”