Eyal Press in The New Yorker:
When Trump kicked off his campaign, last year, he accused Mexico of sending “rapists” and criminals to America. This was a patently outrageous claim, and there was no evidence behind it. According to Robert Sampson, a sociologist at Harvard and the former scientific director of the Project on Human Development in Chicago Neighborhoods, communities with high concentrations of immigrants do not suffer from outsized levels of violence. The opposite is the case. In his exhaustively researched 2012 book, “Great American City,” Sampson noted that, in Chicago, “increases in immigration and language diversity over the decade of the 1990s predicted decreases in neighborhood homicide rates.” Other scholars have turned up similar findings. In 2013, a team of researchers published a paper on Los Angeles that found that “concentrations of immigrants in neighborhoods are linked to significant reductions in crime.” A 2014 study examining a hundred and fifty-seven metropolitan areas in the United States found that violent crime tended to decrease when the population of foreign-born residents rose.
One reason for this may be that immigrants have helped revitalize formerly desolate urban neighborhoods, starting businesses and lowering the prevalence of vacant buildings, where violence can take root. Another possible factor is that, contrary to Trump’s bigoted rhetoric, many immigrants are ambitious strivers, who are highly motivated to support their families and make a better life for their children. Undocumented immigrants may also be more fearful than legal residents of attracting police attention, which could get them deported. Whatever the answer, the research helps make sense of the fact that, during the nineteen-nineties, the foreign-born population in the U.S. grew by more than fifty per cent, and cities such as New York, El Paso, and San Diego, where many of these newcomers settled, did not become cauldrons of violence. They became safer. While numerous factors may have contributed to this—most notably, a stronger economy—it is now widely agreed that immigration played a role, too.