You are what you believe.
At the core of each of us is our belief system. It is around that belief system that a large part of our personal identity is formed. One of the real strengths of fundamentalism is that it provides a stable core belief system. To borrow from 80's new wave and avant-garde band, Talking Heads, “Same as it ever was. Same as it ever was.”
It is much easier to believe you understand who you are and to be stable when your core belief system is stable. For folks like liberals and progressives this is a little more difficult because the walls around our core beliefs are a little less rigid and more willing to flex as new information presents itself. Which means that we, more frequently than fundamentalists, are reshaping our understanding of who we are and how we relate to society, even if in small ways.
For fundamentalist Christians, it is even more complicated than just that. In both direct and subtle ways, they believe their salvation, at least in part, is dependent upon being correct on issues of faith.
Intellectualism invites the constant assessment of the “correctness” of a person's belief system. That's dangerous ground for a fundamentalist Christian. When you confront them on a particular belief you are not only confronting them on an idea that they have held to more rigidly for a longer time than most other folks but you are confronting the very core of who they understand themselves to be. For them, it is those core beliefs upon which their salvation hangs in the balance, at least in part. Questioning it doesn't just question the thought but, for them, it puts into question a lifetime of holding on tightly to that thought.
When you take all of that into consideration, it's really not surprise that most fundamentalist Christians react negatively to or avoid all together any intellectual questioning of their core belief systems. For that matter, it's not surprising that fundamentalist of all camps tend to have a less than positive reaction to intellectualism. They just want to be right and the rest of us just hope to sort out some small version of the truth. A subtle difference but an important one.