Extremism exists in every major faith, and sometimes turns violent
Obviously there are differences. Christians tend to be more concerned with dogma (particularly with the inerrancy of Scripture and such issues as how the Darwinian theory of evolution conflicts with Genesis) than either Jews or Muslims, who are more concerned with the practicalities of being religious in the modern world. But in all three faiths of Abraham, fundamentalism is highly political. Fundamentalists are determined to drag God and religion from the sidelines, where they've been relegated in secular culture, back to center stage.
And in this they have achieved a degree of success. In the mid-20th century, it was widely believed that secularism was the coming ideology and that religion would never again play a major role in world events, but that is clearly not the case today.
In all three faiths, fundamentalists see themselves engaged in a "battle for God." Every single fundamentalist group I have studied is convinced that secular or liberal society wants to wipe out religion. All are rooted in a profound fear of annihilation. The movements begin by opposing members of their own faith and their own people; it is only at a later stage that they turn their attention to foreigners.
Because they believe that they are fighting for survival, fundamentalists tend to militancy, ignoring the more compassionate elements of the faith in favor of more ferocious theologies. In all three religions, including American Protestantism, fundamentalism seems to be becoming more extreme.
Fundamentalist groups and ideologies all tend to follow a similar pattern of behavior. First, they withdraw from mainstream society to form sacred enclaves of pure faith. Obvious examples are Bob Jones University; the ultra-Orthodox communities in New York; and Osama bin Laden's training camps. These fundamentalist churches, colleges, yeshivas, communes, settlements, study groups are fortresses where the "faithful" can live what they regard as a true religious life. They create a counter-culture, in conscious reaction against the modern society, which fills them with such dread.
But from these bastions, fundamentalists sometimes plan a political, military or social offensive. This was very clear at the end of the 1970s, when we saw the Iranian revolution, the emergence of the Moral Majority in the USA, and an upsurge of Islamic and Jewish groups in the Middle East.
Christian fundamentalists in the United States have committed fewer acts of terror than the others for two main reasons: they live in a more peaceful society, which, until last week, was not at war or engaged in a deadly political conflict. Second: the more extreme Protestant groups believe that the democratic federal government of the United States will collapse without their needing to take action: God will see to it. The Christian Identity Groups, a very loose and small network (which seems to have influenced Timothy McVeigh) do sally out of their survival communities in such states as Montana and commit what they regard as acts of war against the godless government and society of the United States: abortion clinics and personnel are often targets.