
By Peter Whoriskey, The Washington Post — Americans have long looked to the decennial census for truths about themselves, and the 1840 version presented them with an improbable and incendiary notion. Slavery was good for Black people, the figures indicated, and freedom led to insanity. Specifically, free Black people were far more likely than the enslaved to succumb to insanity. “Insanity and idiocy” was ten times more common among free…