What the administration said repeatedly was that in light of 9/11, we couldn't risk Saddam staying in power. The harm he could unleash was too great to risk.
The anti-war side then heaps scorn on the very idea that Saddam had any links to al Qaeda. They'd pull a fast one by insisting that there was no evidence that Saddam gave orders to bin Laden, neglecting that the concept of links and support does not have to mean an operational or command and control link. Sometimes it seemed as if the only links acceptable as proof to the anti-war side would have been a video of bin Laden pinky swearing with Saddam to obey Saddam and kill Americans.
But the truth is, Saddam was hip deep in support of Islamic terrorism. And that support included helping al Qaeda:
In his book, At the Center of the Storm, George Tenet details some of the evidence the CIA collected on the relationship between Saddam’s Iraq and al Qaeda prior to March 2003. Tenet revealed that the agency, which was divided on the extent of the relationship, had compiled “more than enough evidence” connecting the two. In other words, contrary to what is now the conventional wisdom, there was a relationship between the Baathist regime and the jihadist terror network. The CIA just wasn’t sure how close the relationship was.
We were right to destroy the Saddam regime. We ended the threat that he wold reaquire WMD--including getting nukes which he was darned close to getting in 1991--and we ended his support for terrorism.
As a bonus, we turned an enemy into an ally, under a democratic form of government that may yet show a third way in the Arab world that ends the choice offered thus far of dictatorship (benign or brutal) and Islamism.
