Unasked Question from Iraq

So the Americans are withdrawing from Iraq without anyone raising the obvious question:
How can it be that a group of politicians (conservatives), ostensibly philosophically opposed to the notion of the ability of government to plan and develop the political and economic structure of a state efficiently and accurately, moves into a foreign state with the confidence that they can completely refashion it from the top down?
And how can it be that a group of politicians (progressives), ostensibly confident in government's ability to plan and develop the political and economic structure of a state efficiently and accurately, opposes that effort to recreate that state with the opinion that such a refashioning can not be done?