First are the hard fundamentalists, those that believe the Bible is literally true (or whichever holy text: the distinction here applies equally to Christians, Muslims, and Jews). Literally true here means exactly that: everything described in the Bible actually happened, down to a great flood and a bearded man with two of every animal in his ark (and, surprisingly, 7 of some of them), seven-days creationism, and all the rest. These people are unserious and honestly, complete and total morons, and they get laughed off the stage by such radical anti-Christians as Benedict XVI. Jewish scholars tend to think this kind of fundamentalism idolizes the Bible - in a bad way. As in "idolatry" and other blasphemies. Let's ignore them.
But second, and far more dangerous, are the soft fundamentalists. While they'll accept that the Bible is full of parables and and fables, meant to teach a moral lesson, they still believe that every lesson in the Bible is morally sacred and must be followed. They don't say that the Bible means what it says, but they say that it means what it means. That means when the Bible says "If a man also lie with mankind, as he lieth with a woman, both of them have committed an abomination: they shall surely be put to death; their blood shall be upon them.," it means it. Honestly, I don't know how to argue with this people, because their arguments make a lot of sense once you grant the premise. If the Bible is a divine gift, how can it be wrong? Not symbolic, not metaphorical, but just flat-out wrong. There's a difference between lying and fiction, and if the Bible so obviously condemns homosexuality, it's either right or wrong. I really can't understand how this kind of prohibition is meant to mean something other than what it facially means, and how a list of commandments is meant to do something other than tell you what to do.
The conclusion of this is that the Bible is either morally supreme, or it is not. And if it's not - if other, non-divine moralities like tolerance for gays or even the abolition of slavery - where does that leave the holy text? This isn't to say that you can't view Jesus as an inspired or even divine teacher of course, but as far as the comparison between soft fundamentalist churches and mainstream churches go, it's tough to undermine the fundamentalist view without undermining the central tenets of faith. This is largely how I end up on the nonreligious side of the equation, because it seems like to go anywhere, you logically have to go so far.