A question posed to me recently.

With respect to growing Christian fundamentalism in America, and theresultant hatred and lack of tolerance towards choice, homosexualityand scientific thought, what's threatening these people's faith so much?

Change. Fear of the unknown. Digression from the dogma spoon-fed at "church". People tend to want to be led, to shepherded, and in general not really think for themselves. Independant thinkers have historically been feared because they threaten the masses with intellectual individuality.
Choice, homosexuality and objective scientific enquiry are contrary to dogma as taught now: They appear to threaten the Bible as it is taught and interpreted now. Very few people actually read the Bible, let alone read it in the context in which it was written: As a series of parables written in a male-dominated, male-oriented, Judaic time, where the masses were generally uneducated and ruled through fear.
This is a very interesting book:
Christianity, Social Tolerance, and Homosexuality : Gay People in Western Europe from the Beginning of the Christian Era to the Fourteenth Century by John Boswell