The primary motivation of jihadists in Iraq is apparently (in retrospect unsurprisingly) ignorance created by anti-American propagandizing in Arab countries.
I've seen several interviews now with U.S. and military personnel in which they describe interrogations with foreign jihadis who are shocked and disillusioned at the reality of Iraq. They've been sold the idea the Americans are wantonly raping and pillaging and oppressing Iraqis (perfectly believable when you've spent the formative years of your life in a madrasah being told Israel and the United States are responsible for all evil in the world), and some jihadis even gave themselves up in disgust when they saw multinational troops were actually rebuilding schools and hospitals, exchanging gifts and smiles with Iraqi kids, and generally working hard to create a better life for the people of Iraq, while the insurgents offer nothing but death and destruction.
We're now reaping the harvest we sowed by tolerating Arab dictatorships that buy off religious extremists (I'm looking at you in particular, Saudi Arabia). That might have been a necessary evil in the Cold War, but there's no excuse for it today. Freedom and democracy are the inalienable right of every human being, and at some level all people know this, particularly in these modern times when clear examples of the kind of lives freedom can provide are available to anyone with a satellite dish or an Internet connection. Denial of these rights inevitably creates resentment, and that resentment will find some channel. In Eastern Europe, it fueled pro-democracy movements that brought down the Soviet Union. In the Arab world, anger and jealousy of the West and frustration with a lack of freedom and prosperity have been coupled with violent religious zealotry to create the jihadist movement. But as with the Communist movement, their vision is a systematic propagandized utopian lie built by a few self-interested cynics to seize power for themselves. That system of misinformation powers the jihadi factory that generates suicide bombings across the world, but as with Communism, discovery of the truth throws a monkey wrench into the gears and will someday (hopefully soon) bring it crashing to a halt. If a free, democratic Iraq can thrive and prosper the example will be obvious to frustrated Muslims and lethal to Islamist ambitions.