When Harold Bloom published The American Religion in 1992, I was a college student at Brigham Young University, and I eagerly bought my own copy at the BYU bookstore. I didn’t always recognize the early, gnostic brand of Mormonism Bloom celebrated, but I knew it was important that finally a cultural critic of national standing saw nothing especially shameful or revolting in my religion’s astonishing nineteenth-century rise. Rather, according to Bloom, its imaginativeness made Mormonism a work of “authentic American genius,” an American original. Like jazz, perhaps.

Yesterday in the New York Times, Bloom returned to his affection for the “genius” of Joseph Smith, but this time in a bloated and...