I don't agree with that at all. Most rural "bumpkin" Churches that you'll find will have solid, basic doctrine. That's why most rural areas vote against the Dems.As does horrible heresy. Simply look at Joe Smith and Charles Taze Russell as well as Mary Baker Eddy.
Whenever I go into a city with 1000+ people in it, the Churches start to go nutty. When an area urbanizes and "educates" itself you get woman preachers and sodomite teachers.
I think the federal-level election maps show that fairly well.