A few years ago, Pew did a poll of Americans to find out how much they knew about religion. This is discussed in the CNN video below. But I can tell you the results: they don’t know much. In addition, atheists and agnostics do better than most religious groups on the test. The reason for both of these results is that in America, the default orientation is religious.
If you don’t think much about religion, then you almost certainly have some kind of warm and fuzzy feeling about a God who loves you and an afterlife that will instill the mess of your current life with meaning and hope. So most of the Christians who took the test were only identified that way in the most casual of ways. Of course, this doesn’t mean that more serious Christians didn’t also do poorly on the test. In particular, even Christians who know a lot about their own religions are often shockingly ignorant about other faiths. A good example of this is the second “difficult” question asked in the CNN segment, “What is the main religion of Indonesia?” I would have thought that this was pretty obvious given the reporting since 911.
Just as the devoutly religious people know more about religion in a general sense, so too will atheists. This is because they think about religion seriously. If they didn’t, they would just be whatever religion mom and dad were. And atheists have another advantage. They tend to learn at least a little about most of the major religions, if for no other reason than that they want to make sure that they too are loony.
So it isn’t surprising that nominally religious people would know little about religion—even their own. And it isn’t surprising that atheists would know a lot about religion. What is surprising is that the United States would be a “nation of believers” when their people don’t give religion much thought.