"Don't talk to strangers" is the advice long given to children by parents of all classes and races. Today it has blossomed into a fundamental precept of civic education, reflecting interracial distrust, personal and political alienation, and a profound suspicion of others. In this powerful and eloquent essay, Danielle Allen, a 2002 MacArthur Fellow, takes this maxim back to Little Rock, rooting out the seeds of distrust to replace them with "a citizenship...