As BOTR says, this is one of the big points that makes the US materially different to the other western democracies. And it does no credit to the US. Americans and America have done some of the most amazing and meritorious things in human history: but on this point there seems a collective refusal to be rational*, at least on this point and maybe on others, that makes one wonder how Americans have functioned as a nation, let alone acheive what they have achieved.
But I wonder if the trouble they are having now (economy, debt, poverty, corporate excess, social division on "right" / "left" terms, healthcare access /affordability etc) are just different manifestations of the same thinking styles that allows such a big and prominant part of the nation to live by an extreme reliance on the existance of God.
People can beleive in God, and yet act and speak rationally. But too many Americans (and an increasing minority following American-style religions outside the US) just don't. Some talk like madmen and twist facts and reason to accomodate God.
Please, this is neither anti-American nor anti-God comment. It is wonderment that a country as advanced and as well endowned in the best of educational facilities (eg: any school in the so-called Ivy Leauge), the most inventive of people (insert list of grand 'only in America' achievements) and the best of thinkers (insert long list) can have this ugly flip side of bigotry and ignorance and credulity.
* I think it takes a heap of rationality to make a success of a big, complex and powerful nation; there may be other ways to either succeed or measure success that don't rely on rationalism at the core. If there are, I don't know of them.