It had nothing to do with logisitics and everything to do with potential threats and possible use of WMD's.
Lets see, the UN had been working since 91 to try and get a handle on his WMD's, he ceased co operation in 98 and by 02 the conclusion was that he was actively making WMD's and the US believed that they may be the victim of a terrorist NBC attack via Iraq's WMD's.
Bearing in mind that about 4000 people had been killed in a unprovoked terrorist attack on US soil in 01, and 88 australians had been killed in 02 coupled with ongoing claims from Al Qaeda that this was just the beginning, and governments were understandably concerned about potential threats to their populations, Sept 11 changed the rules forever and previously accepted doctrines didn't necessarily apply any more.
Plus could the US allow the UN to stubble on for another 11 years and take what they thought was an unacceptable risk to their population from Iraq and Saddam. Would that have been an acceptable timeframe.
Also the cynic in me also said that much of the dithering in the UN was over the recently uncovered "light sweet" deals and ensuring those oil for money deals kept on rolling in.
The timing was Saddams chosing, he could have recommenced co operation with the UN and the US wouldn't have had a leg to stand on.
It comes back to the original issue............the world thought he had WMD's and there was concern that they may find there way into terrorists hands...........The only disagreement was on how to disarm Saddam, the UN wanted the same old ineffective program, the US wanted their own plan.
Now, with the benefit of hindsight, people who once claimed there was WMD's now say there is no justification for the war. You can't have it both ways.