Fundamentalism is a response to bastardized popular religiosity that spread on this side of the pond. In the Roman Catholic Church - the doctrine of papal infallibility defines the final authority on what the religious scriptures say - pretty much in the same way as the US Supreme Court determines what the law says.
But when you have a situation when every schmuck who can barely read thinks that he can also interpret the scriptures and his word is as good as anyone else's word - that is a sure recipe for chaos and undercutting the fundamental feature of religion - the guarantee of certainty. One solution is to jettison mob populism and establish a human authority, pretty much the same way the RCC did. Another solution is to maintain mob populism and fetishize the text itself i.e. vest the final authority in a particular wording of the text itself. Since the Goedel theorem, which basically renders the second choice futile, never dawned on these semi-literate country bumpkins, while mob populism was dear to their hearts, it is no surprise that fundamentalism thrives in the US and for that matter the Islamic countries that are also high on populism.
Wojtek