We can pacify Iraq, but we chose to win hearts and minds rather than subdue a people and exact our due, including respect, obedience, and tribute, as conquerors.
You will notice that under the gentle prodding of Saddam Hussein, the Shia 60% of the population, and the Kurd 20% of the population, relatively quietly bore the yoke put on them by the Sunni 20% of the population.
It is the U.S. renunciation of effective tactics that has emboldened the Iraqis to oppose us. If we want to be successful conquerors, we need to be prepared to shed a little of their blood if they exhibit intransigence. Hussein provided us with a plan, but we in our unenlightened stupidity rejected proven methods, and tried to rewrite the playbook, unfortunately unsuccessfully since our premises were faulty.
We've created a mythology and elevated their religious bleatings as something to which we needed to subscribe. And we behaved as if somehow we violated their delicate sensibilities there would be onerous consquences for us.
Gosh, Hussein's sons and others went around raping women at will, and killing people brutally, and the response was "quiet," the aggrieved seeking to avoid similar treatment at any cost. It is our weakness that has jeopardized our mission, and made the Iraqis bold. A little uncertainty and convincing them that they need to please us or suffer badly would create a much more hospitable environment for us.