Think What Might Have Happened....
If we waited. Really there's no telling. Saddam did have connections with Al Qaeda that are well documented. He had it in for us and he knew his time was coming near.
If he wanted to he could have, and probably did sell or give away WMD to people like Zarqawi, the Doctor, or UBL himself. There are so many other organizations that he could have worked with through borders with Syria and Iran.
I'm sorry, but to wait any longer would have presented an unreasonable risk. Put yourself in the shoes of someone who has to make that decision for an entire country.
I agree that war needs to be a last resort. But at some point, in some cases, you don't have the luxury of using up all your resorts thereby giving the threat a better chance of manifesting.