Mormonism: Treatment Effect Or Selection Effect

David Brooks has an insightful column on “The Book Of Mormon” making the point that stringent, arbitrary, rigorous religious doctrines that liberals find distasteful tend to be both more socially successful and also associated with individuals doing better. What I’m less certain about is the posited causal relationship here:

Rigorous codes of conduct allow people to build their character. Changes in behavior change the mind, so small acts of ritual reinforce networks in the brain. A Mormon denying herself coffee may seem like a silly thing, but regular acts of discipline can lay the foundation for extraordinary acts of self-control when it counts the most.

But is Mormonism giving people self-control here, or are people with a lot of self-control becoming Mormons? Harry Reid is an incredible rags-to-senate-leadership success story and also a convert to Mormonism, but I’m inclined to believe that the same qualities that have made him successful drew him to the Mormon religion rather than the religion drawing him to those qualities. And then of course most Mormons are simply the children of other Mormons who are inhering all kinds of attributes from their parents.