It was a debacle even before Iraq was invaded. The country is in no better shape now than it was under Saddam.
The problem, at the heart, seems to have been a small cabal of men who were torn between two entirely different extremes; on the one hand they wanted to duplicate the exporting of democracy carried out in post-war Europe and Japan, but on the other hand they also wanted to play the game conservatively. Or to put it another way, these were not big men, there were no MacArthurs or Marshalls or Claytons, big thinkers with political masters with, if not the vision, then at least the confidence and intelligence to recognize the vision.
Take General MacArthur, here was a larger than life man, just the kind of man to stare right into the eyes of a God Emperor and tell him what to do, who literally through force of will pushed through a new constitution and government, and more tellingly, an entirely new relationship between a people and that government.
You need big men, and you need deep pockets. Bush was no Roosevelt or Truman, who, whatever else you may think of them, were savvy guys who picked smart cabinets and advisers, and just as importantly gave these guys the latitude they needed. Yes, MacArthur went one step too far and Truman finally had to reign him in, but what MacArthur oversaw in Japan is probably one of the greatest state-building exercises of all time, and what was accomplished in Europe with the Marshall Plan, the transformation in particular of the Western zones of Germany from shattered, smashed and burned post-industrial zone into one of the great economic and political marvels of all time.
Guys like Rumsfeld probably had similar dreams, but they were little men, small, mean people with a audacity, but no coherency of vision, and ultimately insufficient will to impose a vision. They utterly miscalculated the cost of a post-invasion peace, of rebuilding a country brought very low by years of sanctions and a government that pissed what wealth it still had on to the sand.
I don't think Dubya and Rumsfeld should be thrown in chains into a deep dark hole for the invasion. If it had been done properly, much as the use of atomic bombs in Japan in 1945, the moral questions of the initial attack phase would have been largely academic. But it was done wrong, not just wrong but with gross incompetence by men whose ideology and perhaps greed overwhelmed that most critical faculty of leadership, and that is to listen to the experts. They were so busy slapping themselves on the back they couldn't see their own inadequacies. They remind me of the Brits during the Boer War, with a vast military arsenal at their fingertips, but little sense of what the end goal was going to be, beyond vague notions of projecting power and even vaguer ideas that somehow it would all create a more civilized, sensible world.
It wasn't that Bush and Rumsfeld and their other neo-con cronies were bad or evil men, I doubt you could find very many who reaches their high offices who could be considered good or moral in any conventional sense. But what they were were inept. If you're going to mount an invasion, you either do one of two things, you either kill or enslave everyone in the territory you seize, or you bloody well do the hard work and create new governmental systems to replace the ones you broke. You can make the new governing system friendly to your aims, and so you should, if you're going to go to all the trouble of busting the old one, but one way or the other you don't create a situation that is materially worse, and then make-believe that toppling some statues and putting on some elections is a replacement for a properly functioning government and infrastructure.