Looking out over a sea of people in Harvard Yard last week, Mark Zuckerberg, Facebook’s chief executive and one of Harvard’s most famous dropouts, told this year’s graduating class that it was living in an unstable time, when the defining struggle was “against the forces of authoritarianism, isolationism and nationalism.” Two days earlier, another end-of-year ceremony had taken place, just a short walk away on a field outside the law school library. It was Harvard’s first commencement for black graduate students, and many of the speakers talked about a different, more personal kind of struggle, the struggle to be black...