Well, this is the exact policy we followed in Germany and Japan after WWII. And the Iraqi army was not exactly in barracks at the time. They had all gone home. Disbanding them was a de jure recognition of what had already de facto happened.
And they did get paid, after all, unlike the disbanded members of the German and Japanese armies. Bluntly, if 350,000 trained soldiers were actively opposing us, the casualties would have a lot more zeros after them.
