You're right.
But note the difference between Germany, Japan, the Confederacy, and other enemies of the United States in which we have successful built democracies after destroying them. All of those countries had at least a somewhat democratic, liberal history, some real goodwill towards America by a majority of the populace in prewar history, and an enemy that comprised one nation of people. Iraq is a country and a state with at least 3 nations within it. maybe 4, if you count National Iraqi as separate from the Kurdish nation, Sunni nation, and shia nation.
So its not just a matter of committing to a real war vs not.
edit: right, Afganistan thread.
So I'll continue my point and say that though our tactics in Afghanistan aren't as successful as they could be, our small presence is not inflaming the local populace like our larger presence is in Iraq. Maybe the smallness of our occupation there is a good thing.