DrDon and NiteWatchman have got great points here IMO.
In my own experience, I've found that most Fundamentalist and Evangelicals have had a very rough childhood or tragic past / event. They've found something that makes them feel whole, 'better than before / ever' or perhaps in a 'better than others', perhaps not consciously. Now, by no means am I judging them or pigeon-holeing them, but if one were to take away that security, then they'd feel empty or confused again. The concept of 'not knowing' is just too daunting for people to even grasp, that they call the approach of 'not knowing' as 'less powerful' and thus not 'the truth'. But this can be said about almost all interpretations of religion.
That being said, I also find that most people who protect said book with such frantic fervor have admittedly not read the entire book; though always for strange and inconsistent reasons. These are the same people who are branding and telling others that 'their way is the only way'. If only facts, a rational approach and an open mind were enough to have a peaceful discussion without threats and name-calling. As previous posters have wisely stated, perhaps the interpretation of the 'Word of God' really is just a manifestation of the beholder's ego.