I'm tired so I'm keeping it quick today. One of the most fascinating aspects of the modern fundamentalist movements is illustrated in this cartoon over at Answers in Genesis. (I promise I'll start doing creationism pieces soon -- it's a big topic and I could do a year or two just detailing the idiocy there, so be patient.)
Hm. So God exists and Christianity is true because... the Bible says so? You often see this argumentation among fundamentalists, but rarely this blatantly. It's tempting (and sometimes accurate) to think that this comes about from simple weakmindedness, that the fundies simply don't see how circular this belief structure is. But there are other factors at play -- let me briefly discuss a couple of them.
1. Social pressures Fundies often live in a self-contained intellectual world (this is, again, another topic we can go into in detail) and are raised in an environment in which everyone around them is another fundie. Since every person they speak to believes in the self-evident truth of the Bible, it's easy for them to simply accept those cultural values unthinkingly. Unless one is very circumspect about understanding cultural assumptions, this happens to the best of us -- could most of the people reading this argue for the value of, say, artistic integrity from first principles? While these arguments exist, most of us just absorb our matrix of values from the culture at large. (This is one reason why multicultural understanding and integration is so important, but that's a whole other slew of topics not even really related to this.)
2. Conversion experience One of the interesting aspects of the Christian faith is that it emphasizes not so much an ideology as a personal religious experience -- Christians often insist that they personally have spoken with or in some cases even touched God Himself. Indeed, when I myself was converted to Christianity I believed that God was speaking to me, although I believed that he was speaking through the circumstances in my life and through my own understanding of the world rather than through some hallucinatory experience. This emphasis on the personal faith in a Living Christ leads to a certain will to believe in the words that are said to be the words of this "person" whom they now believe to be the Son of God.
To put this another way, when one becomes a Christian it is generally put in terms of a personal experience. Rightly or wrongly, most people who convert to Christianity believe that they have had some sort of personal relationship to Christ. From there, it's easy to see that for a Christian, belief in the Bible is not just a question of vague ideology or abstract theology, but a living, breathing, daily experience. In this context, believing in the Bible is not so much trusting that "well, the Bible says it's true" so much as it is believing that their own experiences in this regard are faulty. Or, to put it another way, they really do believe that they're simply trusting their eyes and their experiences, and that believing that God spoke to them makes more sense than believing in those hard-to-understand equations, measurements, and observations that go into understanding modern science.
This makes fundamentalist thought difficult to combat, as it's based on an explicit belief in a delusional reality. To argue that their beliefs are delusional is insulting and misguided, I think -- better is to point out that the plural of "anecdote" is not "data," and that scientific inquiry is much more intersubjective than their own religious experiences.