Earlier this month, Mayor Zohran Mamdani faced controversy for his appointment of advisor Cea Weaver to run the Mayor’s Office to Protect Tenants. Weaver, X users and the media soon discovered, had made several social-media posts asserting that homeownership was “racist” and “a weapon of white supremacy,” and calling for policies to “impoverish the white middle class.” I dislike the attitudes expressed in these posts. I even think they’re racist. But it’s easy to treat them as aberrant. In fact, at the time they were made—the late 2010s—those attitudes were culturally dominant.Such instinctual, casual anti-white statements reinforced the active institutional...