Perhaps 50 million adult Americans now say their religion is "none" or "don't know." This number has climbed dramatically since the 1990s. About 20 million U.S. Catholics have left that church - so one-tenth of American adults now are ex-Catholics. Two-thirds of American Christians in their 20s drop out of church before age 30, one report estimates. Once-prestigious mainline Protestant faiths with seminary-educated clergy have disintegrated so severely...