Here are some excerpts from an interesting article by Prof. Steven Falkenberg on the nature of religious fundamentalism: http://www.newreformation.org/fundamentalism.htm
The problem with fundamentalism is not that fundamentalists put God first. The problem is that they do not put God first. They put a particular simplistic, limited, human understanding of God above all else. In most cases the fundamentalist understanding of God's will for mankind is that God wants things to be the way they used to be. God's laws are the ones we were taught since we were young. Fundamentalists then become neither Christian or Islam but rather defenders of the culture, dedicated to the preservation of "all we hold dear." In this regard, Christian fundamentalists are a lot more like the Pharisees than they are like Christ. Christ was a cultural and social revolutionary who disregarded the conventions of polite society, broke the religious laws regularly, associated with the "wrong crowd," and generally challenged the emptiness and superficiality of societies' traditions and beliefs. Christ was crucified, at least partly, for being a modernist and an ethical relativist. If Christ came to live among us in the 21'st century, the fundamentalists would have him crucified again, not because they hate Christ, but because they would not recognize him.
A major problem with fundamentalism is that fundamentalists believe they know Gods will for mankind. Fundamentalists believe that they know the truth, that their understanding is 100% accurate and there can be no questioning it and no compromise. Their position is "utterly non-negotiable." They believe they know what is right, wrong, moral, and immoral. As Dr. Neilson notes, this arises from a tendency toward literalism. Literalism, however, is used by fundamentalists as an excuse for the rigidity of their beliefs. They have been told that their beliefs are the truth because they are literal and directly from the Bible and therefore cannot be questioned. There is only one interpretation of the Bible allowed and that is the one they have been taught.
Having strong beliefs is one thing. We all have strong beliefs that we are unwilling to change or reevaluate. Everyone has to have something to believe in and we can't be constantly questioning everything. But where fundamentalism crosses the line and becomes dangerous and destructive is when fundamentalists refuse to allow anyone to have beliefs different from them. It is clearly the case that persons of strong character will refuse to compromise their beliefs. But fundamentalists consider it compromise to let you believe what you want to believe if it is different from their beliefs. So for example, some fundamentalists who believe that abortion is murder are unwilling to allow others to disagree with them. They are not satisfied to refuse to have abortions themselves and to teach their children and fellow believers to do the same, they feel compelled to work to get laws passed which will prevent anyone from getting an abortion. In point of fact, many thoughtful Christians have decided that abortion should be legal, at least in some circumstances. The fundamentalists think those who disagree with them are wrong and some are willing to take extreme measures (terroristic threatening, murdering abortion doctors, bombing abortion clinics, and other terrorist tactics) to prevent those who disagree with them from acting on their beliefs.