It is clear that the terrorists who destroyed the World Trade Center had an economic purpose in mind. There are any number of other buildings in the United States that they could have destroyed, perhaps more easily. They chose the World Trade Center specifically because it was located in the heart of Wall Street -- the preeminent symbol of American capitalism.
In other words, the terrorists were not simply attacking the United States as a political entity. Had they wished to do that, they would have put much more effort into destroying the Capitol, the Washington Monument, the White House or the Lincoln Memorial, to name a few obvious targets. They chose the World Trade Center precisely because they hate capitalism as much as they hate the United States.
This raises an interesting question. Where does this hatred of capitalism come from? Contrary to popular belief, it does not come from Islam. Indeed, one could argue that Islam is the most pro-business of all the world's major religions.
It is worth remembering that the Prophet Muhammad was a businessman, who engaged in extensive commerce during the years before he devoted himself exclusively to religious affairs in the year 611. Even afterward, Muhammad often made comments and took actions that demonstrated his support for business and the free market.
For example, he forbade the imposition of price controls, saying that prices were in God's hands and that he wished to meet God (the same God to whom Christians and Jews pray) without having to answer for some injustice that he might commit in this respect.
Taxation is another area where Muhammad took what today would be considered a very conservative or pro-business approach. He forbade the imposition of special taxes on markets. He called the market "a charitable endowment." Rather, taxes were collected directly from individuals, instead of businesses.
The Koran, Islam's holy book, is filled with passages that can be interpreted as favoring commerce. For example, it says: "O you who believe! Squander not your wealth among yourselves in vanity, except it be a trade by mutual consent. ... And who does that through aggression and injustice, We shall cast him into Fire."
For this reason, scholars have long looked upon Islam as fundamentally pro-capitalism. As Maxime Rodinson wrote in "Islam and Capitalism" (1966), "Economic activity, the search for profit, trade and, consequently, production for the market, are looked upon with no less favor by Muslim tradition than by the Koran itself."
This is one reason why the Muslim world was the most vibrant on earth during the latter part of the Middle Ages. By contrast, Europe was repressed by the economic doctrines of the Catholic Church, which are far more sympathetic toward socialism than is Islam.
But starting in the late 15th and early 16th centuries, Islam and Christianity reversed directions, as regards the economy. Under pressure from a series of invasions, the Islamic world turned inward, establishing fundamentalism as the only permissible religious view. From that date forward, economic and scientific progress in that area slowly ground to a halt. By contrast, the Protestant Reformation freed Europe from the stultifying confines of Catholicism. Many scholars, such as Max Weber, date the origins of modern capitalism and the Industrial Revolution from this event.
Even today, the resistance to modernity, not just capitalism, is intense even in the more enlightened parts of the Middle East, such as Saudi Arabia (as opposed to Afghanistan or Iran). For example, a recent article in The Economist magazine notes that on religious grounds, Saudi judges have banned children's games such as Pokemon, telephones that play recorded music on hold and the practice of sending flowers to hospital patients.
Thus many scholars believe that the hatred of capitalism is less based on Islam's affinity for socialism, than on its fear of modernity. Capitalism is just one of many things that Muslims hate and fear as intrusions upon their religion and their lives. (It is worth noting that there is no separation of church and state in Islamic countries; they are by definition one and the same.) Western science and culture are just as threatening to the stability -- some would say stagnation -- of Muslim life as are Western economic ideas in the form of capitalism.
I think it is one of the world's great tragedies that the Islamic world got off on the wrong track some 500 years ago, in a way that still sows hatred and fanaticism among a few seriously misguided souls even today.