The church isn't losing anybody. The body of Christ is an organism of born-again believers all over the world. God knows who are His. What you are reacting to is all the people walking out the door of the organized religion of Christianity. There is nothing to prove that the "once-Christianized West" was ever comprised of true Christians. It was the fruit of the Christian religion on the culture. It doesn't mean that all those people involved knew the Lord. God is growing His church.