We hear a lot about religious fundamentalism these days. I suppose we are stuck with the term, but it is actually used imprecisely. Fundamentalism, according to one dictionary definition is "strict maintenance of ancient or fundamental doctrines of any religion or ideology." This in itself may not necessarily be a negative thing. Fidelity to a tradition and it's teachings is one legitimate approach to religion. It may be thought by some to be narrow, by others to demonstrate an integrity and clarity of thought.
However, what is often called "fundamentalism" these days is probably better called "triumphalism." This is the view that one's religion is absolutely right, all others are wrong, and usually leads to the conclusion that force is justified to promote one's beliefs. The Buddha condemned this kind of thinking; "this is right, all else is wrong" as leading to disputation and conflict. We can certainly see that today.
The triumphalist imperative pollutes any religion it touches. While it seems more natural to arise in mono-theistic religions ("my god is bigger than your god") sadly even Buddhism doesn't escape. We had the sorry story this week of fundamentalist monks in Sri Lanka breaking up a peace rally with fist-fighting. How anyone can defend this behaviour as consistent with the Buddha's teaching is beyond me.
There is also a Hindu fundamentalism, whose deeds included the assassination of Mahatma Gandhi and the wrecking of the historic Babri mosque in 1992 (which sparked bloody communal riots.) These type of actions are hardly compatible with the Hindu ideal of ahimsa. (harmlessness)
We hear a lot about Islamic fundamentalism (or Islamo-fascism in the fanciful neo-con lexicon.) Often the discussion simplifies complex and contradictory movements within modern Islam, which seems to be in a period of ferment and renewal not unlike the Protestant Reformation of 16th Europe. That period too, had it's "mad mullahs," it's iconclasm and it's struggle to come to terms with a changing world.
Certainly groups like the Taliban, with their ultra-strict moral codes violently enforced, and their wanton destruction of imagery like the Bamiyan Buddhas, and their valorization of war and conflict, qualify as "triumphalist." Some among the Shiites also have a dangerous fascination with apocalyptic thinking; awaiting the end of this world and the coming of the twelfth imam.
The Christians also have a powerful fundamentalist (or triumphalist) wing, especially in the United States. Like their Muslim shadow-selves, they have a very strong belief in the imminent "end of days." It's kind of scary when people who think the end of the world is a good thing are close to the policy making apparatus of major powers.
There is also a Jewish fundamentalism that complicate the Middle-East problem by seeing a religious sanction for occupation of the whole of Palestine to the Jordan. Some of them even want to re-construct the Temple of Solomon, which would involve destroying the Al-Aqsa mosque. To them, a minor detail. To the rest of the world, a major conflagration.
(I'm not aware of Taoist or Jain fundamentalism - maybe I'm just not informed)
These fundamentalisms feed off each other; they need each other to thrive. Where would the Christian Right in the US be without the "evil axis" of "Islamo-fascism" to rant against? Where would the Islamic hard-core get their juice without the "Great Satan" or the "Zionist entity?"
The Buddhist fundamentalists in Sri Lanka are largely a response to the very aggressive and unethical proselytizing of Christian fundamentalist missionaries.
Too bad we can't all just get along.