Unity through faith - many people need to be a part of a group. Religions offer that. The people don't even need to believe in or follow the tenets of the particular flavor of faith. The important thing is to be able to say they are XYZ. It's a label most people can understand. Saying something like "I'm a Christian" is too open-ended. Saying that you are a member of a particular sect is more descriptive.
I'm your huckleberry.