The problem is that the argument for the action has been changing. There has never been a consistent argument justifying the invasion of Iraq.
I would suggest that the emphasis for the action has been changing but not the underlying reason. From the beginning, all the arguments that pop up were made. Overall, the strategy (from the WH perspective) was to remove Saddam and attempt to introduce self-determination to the region as a stabilization tool. Why Iraq? Defiance of UN, brutal regime, WMD --- all were continually stated but these reasons received differing amounts of emphasis throughout the build-up and since then. The emphasis change goes along with the debate -- as objections arose, the facet most related to those objections received more attention. Some call this misleading, some call it changing reasons but the WH laid all these ideas out from the beginning.
Goal: Stabilize the region to protect US interests (both free-flow of oil and breeding ground for terrorists).
Strategy: Remove Saddam, install democracy (in the sense of self-determination). Influence of self-determination will spread and over the long-term, the goal is closer to achievement. For example Iran becomes surrounded by new "democracies" (Iraq/Afghanistan) and movement grows inside Iran.
Reasons for Iraq: US policy of regime change, years of UN defiance seen as evidence that the world will not strike back, belief of possession of WMDs that will be either used on neighboring country (eg. Kuwait) or provided to terrorists, Iraq had been provided support to terrorists (eq. support of Palestinian families), Saddam had demonstrated his willingness for bold action (Kuwait, brutal put-downs of Shia, Kurds).
All of this was laid out by the WH prior to the action in Iraq. Both the reasons and strategy are unique to Iraq. This would not work in Korea since the spread of democracy doesn't have the same bang for the buck potential. Iran didn't have the US policy of regime change, the laundry list of UN violations on the level of Iraq, had not recently taken over another country in the region, etc.
I'm not endorsing the strategy - just suggesting it's genesis.