It's not a matter of WMD. The US had the right under UN resolutions following the 1991 conflict to restart hostilities at any time if cooperation wasn't 100% given. Saddam didn't decide to cooperate, so now ultimately he's going to be brought to justice for his crimes and hanged.
Do you think the police will enforce a search warrant by trusting you to tell them only where to look and where not to look? Sure you can check my palace, but not the basement, kitchen or certain parts of the attic and garage. That's hardly considered an acceptable search. Same for Saddam. Oddly enough in order to have the war a majority of Congress had to approve as well. Bill Clinton agreed the evidence was reputable, and a handful of other people, prior to them changing their opinions to further their ilk's political run.
The bottom line however is intelligence was understood to be fairly certain for years, even before President Bush. He was the only one prepared to attempt to act on that information. Well actually him and the US Congress. More stability will ultimately come of this. Just give it 10 years or so...