May I propose that the most threatening aspect of the fundamentalist elements in the world's religions is that the belief in church-state separation is rejected by fundamentalists. It is replaced by the belief that the state should support one version of religion, the one they practice.
A consideration of this question is appropriate on a God and Science forum because another aspect of fundamentalism is the rejection of established science like the age of the universe or the history of the world and its living creatures commonly called geology and evolution. Thus this discussion could have as well been entitled
"Scriptural infallibility versus Science"
These two elements come together in the United States where the fundamentalists are trying to insert Creationism into academic curriculum. That is a little backwards but not dangerous.
The really dangerous aspect of fundamentalism is the rejection of church-state separation. It means in essence that any nation should have only one legal religion and that all others should be eliminated. Israel is a good example of the clash of two peoples dominated by their fundamentalist elements even though both Israel and Palestine are supposedly secular states. The Jewish fundamentalists are the ones that are trying to take all of that region for the jews, up to the biblical borders of Israel, by the technique of jewish settlements in the occupied terrotories and intimadation of the Palestonians that stand in their way. On the other hand it is the Islamic fundamentalists that rejected last years offer of a peaceful solution because the only solution in their eyes is the elimination of Israel as a jewish state. The fundamentalists on both sides think they have god on their side and that they are just working to attain what god has promised them.
Which brings me to the mainpoint of this post. Islam thinks that god has promised that they would take over the entire world and make heaven on earth by the worldwide practice of Islam.
Indeed up to about 500 years ago it seemed that they might. From the middle east they took over Africa, South Asia including India, Central Asia and Southeast Asia. They were stopped by the Chinese and stopped in middle Europe on Sept 11th, I forget which year. Even Nostradomus predicted that they would take over the whole world. So think that is why the 911 date was picked by the terrorists.
So the Islamic fundamentalists think that the world has been promised to them by god. Yet for the last 500 years they have been back sliding until finally European colonization took over ALL their lands. After WWII the colonists allowed the reformation of Islamic states on the basis of secularism, but at the same time inserted a democratic secular Jewish state right in their midst.
[I do not really understand why there is such an anti-jewish sentiment in Isalm because the Koran says twice that the highest of all people in the eyes of god are the truly religious jews. But that is beside the point.]
The secular democratic west is facing once again a worldwide revolutionary threat. The previous one was godless communism. Ironically this new one is fueled by a strong, extreme belief in god and what god has promised. For the time being the numbers of Islamic extremists are too small to threaten the entire world. But the 911 attack, designed to suck the US into attacking Afganistan, and the subsequent killing of many Afgan civilians as the Taliban troops hide in Mosques and schools, is a very clever and bold plan to turn all of Islam against the west. So far evrything seems to be going according to plan- their plan.
So this forum has included many discussions between secular scientists and unscientific fundamentalists who base their beliefs on rigid literal belief in scripture. I see the latter as one of the most fundamental problems of this nation and the world, and of course the basis of Islamic terrorism. The final challenge of science is to overcome the unscientific beliefs of so many, actually well-intentioned people. Science and god can coexist, but not if scripture is taken literally. So in the long run it's a fight between science and fundamentalism for the mind of mankind.