Even air dominance doesn't answer every question, or else the insurgent phase of OIF would have been settled by it alone.

There's no rational argument in the idea that the Coalition partners could have hiked on foot into Baghdad or into Basra, or trucked in unfazed, and once the Iraqis had melted into urban areas and waited to trip the next phase into counter-insurgency warfare, armor was certainly used to quell the groups when it shifted into particularly gnarly street fighting. Some of the worst resistance came from the Fedayeen forces who weren't even necessarily the best trained, but the most ideologically committed, and as much trouble as they gave, if adopted better strategy could have probably held up Coalition timetables even more- and that's with armor sent in.

Ask yourself this: suppose you are an army chief of staff. Are you sure you would take the risk both with your own career and reputation and the fate of your countrymen and forgo the use of armor? Sure you would feel 100% confident with that decision? How would you explain that one if your decision turned out to be wrong?

As it was in Somalia a decade earlier.