There was a pretty good programme on PBS two nights ago that I caught in the hotel room about the insurgency, and the reasons they fight. They had reporters interview them, and tag along, etc. It's available as an online stream, I'd watch it if you have the time.
http://www.pbs.org/wgbh/pages/frontline/insurgency/
It makes things seem a little more complicated than that six-month-old article would appear to suggest. An interesting interview was with a Sunni army officer who thought the US really did need to stay for a while longer, because bad though things may be right now, it is infinitely preferable to what would happen otherwise. In other cases in the last 15-20 years, from the Balkans, East Timor, and whatnot when there have been genocides and other forms of civil war, there have been calls to send the military in to quell the fighting. Why would such not happen if the coalition forces pulled out and Iraq started its own genocides?
NTM