The problem of course is what was a valid reason (to strip Saddam of WMD's and stop him from getting the nuke) was incorrect. Not only incorrect but based on reporting since the decision to invade, it's come to light that intelligence was cherry picked to prove the presence of WMD's. That's kind of a big deal and well beyond a change in stance in regards to foreign policy.
You seem to strip the decision to go to war of basically everything of meaning in order to present Iraq as some natural flow of foreign policy. Some inevitable branch off of the 9/11 attack.