Claiming some sort of pre-emptive invasion to keep Saddam from misbehaving is a crock. As it was, he was unable to restart his nuclear, biological and chemical weapons programs due to the embargo. We should have stuck with enforcing that, for as long as it took, while we finished the job with Al Qaeda elsewhere. If it turned out later one that Saddam was working with Al Qaeda, or that he was actually able to restart any of his weapons programs and refused to stop when he got caught at it, then we might have had a valid pretext for an invasion. As it was, we did not. And, I know, some folks claim Saddam was in violation of UN resolutions so and so, and point at that for our justification, but these same people are full of crap if they do not point out the many and various UN resolutions Israel has violated over the years and espouse the same treatment for them.
Now let me ask you a question - why do you suppose we did not completely finish the job in Afghanistan, then put as much time and effort into rebuilding their country as we have in Iraq (which, by the way, was supposed to pay for its own rebuilding with oil revenues).