Because it gives meaning to life, that’s why.
It’s a commonplace to anyone who’s studied the rise of fascism, of which Islamofascism is the most recent variety. The main problem with democratic capitalism is that it’s so successful, and therefore very boring. A generation or two of European intellectuals bemoaned the great triumph of science and industry, which they portrayed as relentlessly stifling the human soul, burying us under a hill of material things.
The Germans produced the most moving such literature — think Nietzsche, think Hesse, not accidentally the cult hero of the American revolt against materialism in the 1960s — and, seeking for paths to spiritual fulfillment, they often wandered off into Eastern mysticism. (Californians dd, too, and sometimes still do, but that’s not fascism. It’s Hollywood spirituality).
The spiritual path merged with politics, catalyzed by war. All fascism, whatever version of social or political organization it advocates, insists that war is the true measure of human virtue. A person’s valor and courage are measured by his performance in combat. The Italian fascists insisted that Mussolini and his followers were superior people who had been molded in the trenches of the Great War. Young men and women who believed they possessed heroic qualities raced to join the fascist movement, just as they now race to join the jihad.
It is not primarily a matter of social class, although there is a considerable literature on the recruitment of poor young Muslims to suicide terrorism, in which the recruiters offer money and security to the surviving family. The primary passion is excitement, the thrill of fighting the enemy, of making a signal contribution to the creation of a new world, and joining an irresistible force.
How much more thrilling than plodding along in a bourgeois world with no spiritual fulfillment, but only…things.
This quest for the meaning of life is a leitmotif of human history. The British Empire was replete with them (Lawrence, for example) as was America as we marched West to fill out the continent. Modern politics has enlisted such people in an enthusiastic mass movement that threatens democratic capitalism. The 20th-century fascists were largely secular, substituting their own rituals for traditional religious ones; Islamofascism turns it around, substituting religious rituals and beliefs for the largely secular ones that defined the “modern world.”
Both work so long as the movement succeeds. Both fail when they are defeated. That’s why we have to crush the jihad — we kill the jihadis before they kill us, and we shatter their ideology by demonstrating that their leaders are false prophets.