Commentators on MSNBC and CNN have been shedding crocodile tears over Donald Trump’s “divisive rhetoric” and lamenting his failure to unify the country. This sudden concern for national unity is rather hard to take from the same worthies who have incessantly glorified the Black Lives Matter movement over the last year and a half. Let’s dip into the rhetoric of a garden-variety Black Lives Matter march that I observed last November on Fifth Avenue in New York City. It featured “F**k the Police,” “Murderer Cops,” and “Racism Is the Disease, Revolution Is the Cure” T-shirts, “Stop Police Terror” signs, and...