So thinks Catholic University philsophy prof Bradley Lewis. Here is his understanding of how the just war criteria in the CCC (2309) are applied to the Iraq war:
Lasting: Saddam had been in power and causing misery and death for three decades, and his sons appeared to be next in line to continue their father's "work". And if we're going to use hindsight to throw out the WMD rationale, how about including, then, the corruption of the UN through the Oil-For-Food scandal, where a rogue state was able to use illegal cash to bribe the very body that was supposed to be monitoring its compliance.
Grave: If you look at the list above, even if you strip out items b) and c) having to do with WMD, you still have a pretty compelling set of reasons. Especially the hundreds of thousands of Iraqi citizens who had been systematically killed and oppressed.
Certain: Again, even setting aside the WMD issues (which seemed certain to everyone at the time), there is no doubt that Saddam would continue his nefarious behavior.
Impractical: Saddam was a murderous tyrant. What means, other than war, have been used successfully to stop such people?
Ineffective: We had tried economic sanctions, military no-fly zones, embargoes, diplomatic isolation, targeted strikes, inspection regimes, etc. etc. etc. We had tried to get Saddam to comply for more than a decade, and to no avail.
Prospects for success: No one ever doubted that the Coalition could win a war. And with good reason, in retrospect...
Proportionality: There can be no debate on this criterion; the data simply don't support any other conclusion. As MOJ points out, according to some (non-Bush-friendly) sources, there were fewer than 20,000 civilian deaths in Iraq in 18 months. That was an average year for Saddam's regime, according to some authorities. In addition, the technological capabilities of the US made proportionality more feasible. The ability to target precision weapons sharply reverses a millenium-long trend toward more collateral casualties, and broadens the scope of a just war.
Based on this analysis, the war appears to be just. Moreover, I have never read an analysis of the Iraq War which directly applied the Church's just war criteria and come to the conclusion that the war was unjust. (Please send me a link if you have seen one.) Most people simply believe the war has to be unjust, and assume the Church's teaching has to support this position.
But an assertion is not an argument. And I believe the most negative thing you can say at this point is that the war may be unjust, but the question is inconclusive.