Fifty years ago, the majority of American Catholics confessed their sins regularly to a priest. But now only 2 percent of Catholics go regularly to confession, and three-quarters never go, or go less than once a year. To traditionalists, this might seem like a sign of decline in the post–Vatican II era. But according to John Cornwell, author of “The Dark Box: A Secret History of Confession,” this isn’t the first time Catholics have largely abandoned confession. The practice has evolved dramatically over the centuries, from a rare communal event to a regular private one. Cornwell thinks it’s time to reform confession again, in part because he sees it as a key—and underappreciated—enabler of the sex-abuse scandals that have rocked the church