Your analogy of the occupation of Germany and Japan after WWII is good. Another good analogy in favor of war with Iraq is: the actions (or nonactions) of France and Britain in 1936, when they failed to respond to the Germans in the Spanish revolution, or 1938 when they did nothing to prevent German annexation of Austria. Had they acted, the bloodshed would be less than it turned out to be.
However, I do not think the US of today has the stomach to occupy a country like we did after WW II. Also (and at the risk of sounding culturally biased), I think certain cultures are beyond help--Haiti is an example of this. We have intervened there twice since the early 1900's and nothing has changed.
If we are going to occupy Iraq, we should at least have this discussion about the price now. Otherwise, there will be great pressure to withdraw and we will leave behind a government that could be as potentially as bad as Saddam's.
I agree that such discussion would be a good thing -- especially if it includes ample consideration of the price we could pay for not occupying long enough to oversee transition to a stable regime, one that is in formal alliance with us.