Just because someone is an atheist doesn't make them an open minded person. Just because they've dismissed theistic religion, doesn't mean that they don't subscribe to other nonsense. Such as racial supremacy, and nationalism. Which is very apparent in countries such as Norway, or Sweden.

The reason atheists are usually the smartest of the bunch, is because it takes a deal of open mindedness to go against the social norm. The norm being Christianity, in America. And if you're closed minded, then you're likely to be religious. But merely for traditional reasons.

Now, if atheism was the social norm, then closed minded people would be atheists, and wouldn't give that label a second thought.