In case you needed another another reason

From the mouths of the soldiers on the ground:

"Take us out of that vacuum -- and it's on the edge now -- and boom, it would become a free-for-all," said Lt. Col. Mark Suich, who commands the 1st Squadron, 89th Cavalry Regiment just south of Baghdad. "It would be a raw contention for power. That would be the bloodiest piece of this war."

Well, no kidding. That's what I've been saying from the start.