As an act of iconoclasm and with some degree of irony, it's not to uncommon for one to quip that Christian fundamentalist movements are thoroughly post-Enlightenment and post-rationalist in nature. Modern fundamentalism, for all its emotions, spiritual convictions and arrational revelations has deeper and more explicit roots in rationalism than any brand of Christianity before. For centuries, religion and scientific inquiry, despite their potential awkward cohabitation survived quite well together, but as soon as fundamentalism took up the framework of rationalism to make its case, the two have been in active contradiction.
When genuinely critical Biblical analysis was set in motion after the Enlightenment, particularly in the German-speaking world, religious conservatives, instead of shrugging it off as the Modernists would do, retorted with the the Bible itself. To these budding fundamentalists, the Enlightenment intelligentsia made the critical error of categorically ignoring or brushing aside the miracles and the inconceivabilities of the Bible; to them, the Bible should be considered yet another article of evidence.
Sociologically, this was not so mportant in its boldness, but it signaled the first step by fundamentalists into the realm of critical rationalism, a step that milder brands of Christianity have not dared. To the adherent of a vanilla Mainline sect, religion functions as little more than a cultural tradition. Religion may be important for cohesion, identification and imprinting the young with moral justifications, but fundamentalism ties those factors to an clumsy, although extant empiricism.
The goal of fundamentalism was to justify the Bible not so much with arbitrary authority, but with evidence and in deductive and irrefutable means. A sardonic secularist can deride the whole enterprise, but the effort cloaked fundamentalist apologetics forever in the garb of scientific rationalism.
The non-religious typically openly scorn most fundamentalists for their ridiculous and improbable beliefs, which is in a way quite justified, yet they more often than not neglect to realize that although literalists carry a weighty load of cognitive dissonance, their emphasis is one inherently one that is empirical.
Other Christians with liberal and singularly metaphoric readings of the Bible can weasel out of critiques of their religion by invoking what they see as the unimportance of the stories such as the ark, the immolation if Jepthah's daughter, the conquest of Canaan and the resurrection to the spiritual validity of Christianity. These "believers" are the ones whose religion is nothing more than vague emotions tied to their inherited cultured celebrated solely anteritiy's sake. They do not pretend so much to have an empirical basis for their credulity as do fundamentalists, and thus they are at all times absolutely unmoved by reason.
Biblical literalists and scientific naturalists are however on the same epistemological page. True to their name, fundamentalists include the factual claims of the Bible as fundamental to its truth value. They admit as do naturalists that a book which could not get the facts right cannot be trusted to get spiritual truths right as well. Of course their devotion to the spirituality of their faith keeps them from being able to admit the factual deficiencies of the Bible, but their ideology still requires them to actually be able to treat their assertions as something theoretically disproveable.
Non-fundamentalists invent for themselves an even more loopy world in which physical and spiritual realities are unimportant. Not only in this worldview is the factuality of the the Bible unimportant but to them it often seems that there is no even pretended connection between what they believe and reality. Some aligned with New Ageism go as far as denying objective reality all together while asserting bland and unprofound sophisms to justify people who believe for no analyzable reason.
This is why it should be evident to any naturalist that non-fundamentalists are so much more intellectually worthless and dangerous to the popularization of scientific knowledge.
There is an idea that fundamentalism is simply religion in its last throes attempting to radicalize itself against the scientific knowledge and the global community which is gradually rendering the explanatory purpose of religion obsolete. There may be some validity in that view, but even more important, I think is the overlooked fact that fundamentalism is the closest religious thought has ever gotten to naturalism on terms of their preliminary assumptions of reality. They have grown to be primarily concerned with the factuality of beliefs and the links between morality and the real world. For them, there may indeed be a strong distinction between the physical and spiritual, but they acknowledge that one cannot ignore physical reality when making claims about the perceived spiritual or moral state of things.