Odd religions and IQ: The discussion of Mormonism connected to Romney's run for President confirmed what I had observed before: lots of people assume that members of small, odd religions must be dumb. How else could you believe that stuff? Well, data have a way of disconfirming as well as confirming stereotypes.
The General Social Survey, unfortunately, throws together many of these smalls sects into the generic "Protestant" category, so I will have to use the question about which religion you were raised in, on the assumption that most people do not switch. For some reason, they give a more specific breakdown with this question. Shown below are mean IQs for whites, and I've included some mainline churches for the sake of comparison:
Mean IQ for whites
United Methodists 101.8
Southern Baptists 98.0
Assembly of God 94.5
Episcopalians at the top is a real shocker, and other mainstream churches are also above average. But people who didn't know better might surprised to find that, in terms of intelligence, Mormons are very much like these other groups. They are not similar to Pentecostals or members of the Assembly of God, as the numbers above indicate. You can see a bit of a North-South contrast here, and Mormons are northerners. They are heavily English and Scandanavian.
While you can find exceptions, evangelicals and fundamentalists don't believe in things that, to a mainline Protestant, are completely from another planet, yet these groups tend to have below-average IQs. Mormons, with beliefs that make some people really flip out, are a relatively smart group. There simply is no strong correlation between the perceived strangeness of beliefs and IQ. I'm sure many people think it's crazy to circumcise infant boys, but in case you haven't heard, Jews are smart as hell. (Keep in mind that samples are smaller than they should be for the small churches. Also--while a skeptic can claim that many of the smart folks have left the odd churches of their childhood, research shows that most Americans don't switch, and a child's IQ is positively correlated with that of his parents.)