The most plausible explanation is offered by my friend Gabriel Andrade:
In this discussion, it is pertinent to present the figure of Sayyid Qutb. The renewed Muslim fundamentalism in the late twentieth century owes much to this character. It was he who, in the mid-twentieth century, launched the movement that later would lead to the Muslim Brotherhood, and would then give ideological ammo to groups like Al Qaeda and Islamic Army.
It is true that Qutb, whose work is vast, never made a call to kill innocents using terrorist tactics. But he did make a call to destroy the West. Long before Samuel Huntington made popular his thesis about the clash of civilizations, it was Qutb himself who hypothesized that a confrontation was inevitable. Why was it necessary to destroy the West? Qutb does not offer the typical responses of the leftists (in fact, he was executed by Nasser, a dictator pretty much spoiled by the left!). For Qutb, invasions, supporting dictators, and the exercise of imperial power, is just a minor reason. The real reason for his crusade is the moral decline of the West.
Qutb was visiting the US, and he was horrified to see that adolescent boys were dancing with the girls (this was mid-twentieth century, certainly today he would be more horrified with reggaeton!). From that very traumatic experience, he wanted to save the Muslim world from Western depravity. His enemy, then, was not just the US, France or England, typical imperial powers. It was also Switzerland, Luxembourg, Andorra, small countries that do not exert any imperial predation, but whose culture is offensive enough to warrant their destruction. Why did Muslim fundamentalists place a bomb in a nightclub in Bali? Has the Indonesian government extracted oil from other Muslim countries they invaded? No: the terrorists placed a bomb at the club, precisely because they hate clubs!
The fundamental error of leftists like Chomsky is not realizing that the values they defend, are a source of hatred for the Muslim fundamentalism and that the imperial predation is just a minor reason. The traditional left has advocated a secular state, the promotion of science, women’s liberation, sexual liberation, artistic creation, etc. The Muslim fundamentalism hates all that. Mark Steyn summed it up very comically like this: the jihadist will be very willing to kill Susan Sontag (a prominent American leftist) before she has enough time to say “But wait, I’m on your side!“.
In one sentence, it is the hatred of freedom.