Yesterday I reported Putnam and Campbell's finding that when people find their politics and religion out of alignment, they tend to change their religion. I don't want to leave that finding out there for a merely cynical interpretation. People choose their religions for religious reasons, and the more religious they are, the more true that is.
Putnam and Campbell found that at the macro level there is a clear correlation between political ideology and denominational choice. Yet they did not see the same thing on the micro level, at least not at first blush. When people explain why they chose their religious institution, they give religious reasons; the more religious they are, the more true this is.
Putnam and Campbell square this seeming contradiction this way. People with no religion leave formal religion because they don't like all the politics, so they do not show up in congregational studies. People who choose conservative faiths do so to fight moral decay, which they do directly through the theology of their faith, and only indirectly through politics.