Iraq broke the peace agreement.
We had every right to go in.
It was the UN that was balking (France and Russia) because they were getting illegal oil.
Sadaam had to prove to us that he didn't have WMD's, we did not have to prove he did to invade.
Even though we had every right to go in, did we have a compelling reason to invade at a cost of several thousands lives and hundreds of billions of dollars apart from the threat of WMDs?