The war was never about finding actual WMD in Iraq, it was about enforcing Nonproliferation policy, and ending the Baathists' ability to obtain WMD's, forever.
UNSCOM already got rid of >90% of Iraq's WMDs, according to the UNSCOM inspectors themselves. However, while the UNSCOM inspectors successfully dismantled Iraq's nuclear program (6 months from fielding nukes before GW1 started), and virtually all of its bio/chem program, every UNSCOM inspector, from Hans Blix to Scott Ritter admitted that UNSCOM (and UNMOVIC) were unable to rid Iraq of the documents, plans, blueprints, and other knowhow that would allow Iraq to rebuild its WMD programs within 3 to 4 years after the UN lifted sanctions. Hussein had demonstrated an unwavering desire to obtain nukes and WMD, and had shown he was willing to thwart the UN in order to further that goal. That combined with his rampant obstructionism during the inspections undermined the US's confidence that UN had successfully neutralized his threat. Additionally, Saddam is on record stating that it was his destiny to lead the Arab world in a nuclear war against Israel.
The US had only two options to realistically deal with this problem: Leave Hussein in power, and prevent him from acquiring WMD material by tightening sanctions... or depose him. Sanctions were hurting the Iraqi people much more than Saddam, and the UN was already buckling on sanctions anyway. That option wasn't going to last, and with the UN out and Iraq's weapons programs at full steam again by 2008 (with French help again, possibly, remember Osiraq), Iran would have no choice but do likewise. An Iran/Iraq bilateral wmd arms race would have sucked in Saudi Arabia and forced Israel to further increase its nuclear deterrent, which would in turn have sucked in Egypt, Syria, and perhaps even Jordan. Voila, the entire Middle East is nuclear, and a hairtrigger (a terrorist nuclear attack on Israel, most likely) away from glassing the world's oil supply. Is that what you detractors really want?
The only real choice here was to get rid of Hussein, and install a govt. that would adhere to the Nonproliferation Treaty.
I disagree with Bush selling the war on the presence of WMD, as I've always thought there are truly none to speak of. UNSCOM did its job well, despite persistent Iraqi deception and obstructionism. Bush was, imo, disingenious, and he should have just told the truth and trusted the American people's common sense and judgement. But the threat of WMD proliferation represented by Hussein's regime was all too real, albeit a harder political sell. Regardless, it was wise to do, and now Nonproliferation policy has been restored, has teeth, and has put other lunatic dictators on notice *cough*kimjongil*cough*. This is a good thing for the security of both the US and the world.
For those who need links and quotes:
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http://www.thebulletin.org/issues/1998/mj98/mj98albright.html
David Albright, nuclear physicist & UNSCOM inspector:
Even as Iraq was agreeing, under the terms of Resolution 687, to disclose its nuclear program and bring it to an end, it was developing a broad strategy for hiding evidence of the program and misleading U.N. inspectors about it.
...
In 1998, many believe that Iraq?s nuclear program has been dismantled and most if not all of the materials and equipment that were used in that program have been found and destroyed. But in a seven-year-plus effort, U.N. inspectors from the U.N. Special Commission (UNSCOM) and the International Atomic Energy Agency (IAEA) Action Team have had to work through so many layers of deception, and have received so many different ?full, final, and complete declarations? from the Iraqis, that they have no doubt Iraq is still hiding important information. Inspectors believe they may never know the full story.
And theirs is not idle curiosity. The stakes are high. [bold]Inspectors believe that Iraq could reconstitute its nuclear weapons program quickly, once sanctions are lifted. Although Iraq might need several years to recreate its enriched-uranium or plutonium programs, it might be able to acquire fissile material on the black market. In that case, it has already learned enough to be able to build a nuclear weapon in less than a year.[/bold] As a result, Iraq?s nuclear potential must be carefully scrutinized by international inspectors for some time to come.
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http://www.pbs.org/wgbh/pages/frontline/shows/unscom/interviews/ritter.html
(read the part about the Agricultural Ministry)
http://www.nuclearfiles.org/hinonproliferationtreaty/index.html
http://www.thebulletin.org/research/collections/iraq.html
There's plenty more, just Google Rolf Ekeus, Richard Butler, Hans Blix, Scott Ritter, David Albright.