"Harvard political scientist Robert Putnam – famous for 'Bowling Alone,' his 2000 book on declining civic engagement – has found that the greater the diversity in a community, the fewer people vote and the less they volunteer, the less they give to charity and work on community projects. In the most diverse communities, neighbors trust one another about half as much as they do in the most homogenous settings. The study, the largest ever on civic engagement in America, found that virtually all measures of civic health are lower in more diverse settings."
"However, recent theoretical and empirical work has uncovered a community-diversity dialectic wherein the contextual conditions that foster respect for diversity often run in opposition to those that foster sense of community. More specifically, within neighborhoods, residential integration provides opportunities for intergroup contact that are necessary to promote respect for diversity but may prevent the formation of dense interpersonal networks that are necessary to promote sense of community."