You actually hit one nail right on the head: the fact is that a large percentage of Iraqis, especially in the "Sunni triangle", depended on the regime for their livelihood. Nationwide there are 3,000,000 former Baathists, with a disproportionate share of the hardcore members to be found in places like Tikrit. I doubt many want Saddam back in power, but they clearly have no love for Americans, and if events continue to suggest we can't control the violence, have no doubt they'll start assisting the insurgency. At the back of their mind is the fear that somehow, Saddam might be resurrected, if only in central Iraq. Choosing sides in this uncertain environment is a no-brainer: if they assist the rebels, the Americans will still pussy-foot over stronger retaliation against pro-insurgency communities, yet if they're seen to collaborate with US forces, they'll be the first ones to enter the torture chambers if a Saddamite order is even partly restored.