I think we're getting offcourse. No one's saying we shouldn't be proactive against terrorism. At least not from our vantage point. I'm certainly not a pacifist. I think, however, that with regards to the Church teaching on "just war" we have to be careful not to open up a Pandora's box. Hindsight is 20/20, but I wonder how many believe we made a mistake by blockading Cuba instead of starting a nuclear war with the Soviets during the missile crisis. The war in Iraq is a lot trickier, and the Pope certainly isn't speaking with infallibility when he or one of his associates is opining on Iraq, but we would do well to consider their reasoning - not necessarily agree - but explore the ramifications in totality before going to war.
Now, that said, I believe we did explore the ramifications completely. I believe the opinion of the Vatican is wrong on this. It's not a matter of faith, but it's a matter of conscience.