In 2004, when the comedian Dave Chappelle performed at UNO Lakefront Arena, he asked a white guy sitting in the audience to imagine that he and Chappelle could take a time machine back to colonial Virginia. He asked him to imagine them stepping out onto a road just as George Washington was approaching. "You might say, 'Look, Dave, there's George Washington, the father of our country. Let's go say hi.' And I'd say, "Run! It's George Washington!'"There might not be a better explanation for why some black Americans look askance at white Americans' heroes. How much should it matter to...