Concerning the terrorists' side: the attack on rationality in question is not exclusively religious.
As much as I detest religious fundamentalism, it has more of a secondary role, particularly an attack like last thursdays. The "soccer ball" faction likes to underline the reactionary nature of fundamentalist Islam, and to tie it to the different terrorist activities.
But the religious fervour comes 2nd, providing a bind, a pretext, a deep well of irrationality, certainty and justifications from which to pick, but anyone who thinks bombs went off because these people didn't like the short skirts, booze and pop music we have in the west is another kind of loony.

If you are pushed to bomb people, out of reasons X or Y, it's a natural human instinct to hunt for rationalisations and to somehow make it fit into your moral universe. Of course, we kid ourselves into thinking it's the other way around, hence the confusion. A direct word from God is a pretty good justification...

Many people have recently pointed out the nationalist or political dimensions of the attacks..
For example see the fantastic Karen Amstrong who knows a thing or two about fundamentalists.

There are too many lazy, unexamined assumptions about Islam, which tends to be regarded as an amorphous, monolithic entity. Remarks such as "They hate our freedom" may give some a righteous glow, but they are not useful, because they are rarely accompanied by a rigorous analysis of who exactly "they" are.

The story of Qutb is also instructive as a reminder that militant religiosity is often the product of social, economic and political factors. Qutb was imprisoned for 15 years in one of Nasser's vile concentration camps, where he and thousands of other members of the Muslim Brotherhood were subjected to physical and mental torture. He entered the camp as a moderate, but the prison made him a fundamentalist. Modern secularism, as he had experienced it under Nasser, seemed a great evil and a lethal assault on faith.

Or Juan Cole:

Zarqawi's Salafi group would never celebrate "Arabism" or speak of "heroes" (abtal) when referring to the "holy warriors" or mujahidin. Urubah and batal, Arabism and hero, are typical of the vocabulary of secular Arab nationalism-- in, say, the tradition of Gamal Abdel Nasser. That message is coming from a group of terrorists that is much more comfortable with this language than are typically the extremist Salafis like Zarqawi. "Hero" would sem a term of humanistic pride to them, and Arabism would seem narrow and idolatrous as a competitor with Islam. There are Muslim thinkers who meld political Islam and Arabism-- this is common in Egypt, e.g. But they belong to a different religious and intellectual tradition than Zarqawi.

They are not trying to create religious but good old nationalist irrationality, the kind that leads to divisions and wars.

You're either with us, or against us.