Like a sitcom in its death throes jumping the proverbial shark, the cancel-culture movement is plunging into a humiliating depth of inanity. This weekend, video emerged from a person called Frederick Joseph, a regular practitioner of “man on the street put-up jobs,” showing a confrontation with a white woman named Emma Sarley. Sarley supposedly told Joseph, who is black, to “go back to [his] hood.” Or at least that’s what he says. She doesn’t say this on the video. The familiar fracas ensued: Social-media mobs assembled, and quickly Sarley was fired from her job. But what happened next was a...