Secretary of State Antony Blinken is poised to further aggravate the controversy over racism and human rights in U.S. foreign policy that he stirred this week. Earlier today, according to Politico, he issued a cable to American embassies worldwide, encouraging diplomats to reckon honestly with the darkest chapters of U.S. history. “That means we acknowledge our imperfections. We don’t sweep them under the rug. We confront them openly and transparently,” he reportedly wrote.

It’s only the latest episode in a months-long debate about how Blinken and his colleagues talk about racism and discrimination on the world stage, including when face-to-face with …