Even if I did believe the intentions of the US and allies were as entirely honorable as you have outlined, it would have to be the stupidest tactic to tackle terrorism I have ever heard of!
Iraq was one of very few countries in the region that did not have islamic or fundamentalist controlled government. Hussein may have been a brutal dictator but he kept the religous fundamentalists in check.
Now it's open season and the Iranian leaning Shite fundamentalists who want Islamic law would win elections in a landslide. Great plan!
If there are no elections than we'll have civil war!
Associating Iraq to the war on terror was a very big mistake. Continuing to keep it as such only compounds it.