fundamentalism is faith in it's purest form. fundies build their lives upon their faith. every single move is faith-oriented. a bible-under-the-arm-christian who goes by the letter might be viewed as fundamentalist by liberal jesus-loves-you-christians but in the end the former is more honest, more true to his belief.
now if someone, who knows religion in it's purest form - which usually coincides with it's most horrible form - finds out that it's all full of rubbish - and this is far from being a rapid process, it may take years and decades full of doubt, anger, depression and sleepless nights to come to this conclusion - you can't just sell that someone your next best religious flavour.
if you think, the bible is true to the letter, you can't love god. the bible's paints a monster of a god. you can't possible like, less worship such a god - a mass-murdering, anger-laden, nationalist, unjust, completely insane maniac.
if you think, the bible should not be taken literally, well... what's left for your christian faith? what's the base? if you just pick some verses about love, you might as well take some humanist literature and drop the bible and it's sick superhero.
if you read the bible, you can't believe in it anymore. if you drop the bible, you can invent your own god, but you know it's just invented. which makes you pretty much anything between a deist and an agnostic. once you turned agnostic you might as well call yourself an atheist. because if you can't know anything about a god, why would you believe in one?
the USA have a high religious tendency as of lately. i heard it's not allways good to declare yourself an atheist publicly (and why would one do that anyway). and stats always lie.