Saddam's regime was talking out of both sides of it's mouth at the time;
in order to keep the Americans off his back, (which didn't work, but...) he was telling them, and the international inspectors, that he had disposed of all his chemical weapons- almost all of which had been American made to begin with;
but in order to avoid his neighbours trying for Iran-Iraq Round 2, he was telling most of the rest of the middle east that he still had a chemical weapons program.
Trying to preserve deterrence, giving out both stories, and also trying to persuade the rest of the Arab world that he was lying to the Americans- and they had enough technical intelligence to know that.
What happened to Iraq is the actual real world resolution of the liar's paradox; when you tell someone "I am a Liar," we know now they do believe you that one time- and that one time only, and assume everything else you say is raving bullshit.
Now think on; what happens in an army in a state run on that principle? A lot of the missed opportunities to use them, some of the failed calls for chemical support that turn up in the leaked documents, are down to the fact that the Iraqi army had got itself lost in the hall of mirrors and much of it's own command didn't know whether it had chemical weapons or not.
So much had actually been destroyed, so much of what was left had been hidden from the inspectors, then hidden from the hiders, then bureaucratically lost, then scarphed as part of someone's private fiefdom, then mislaid, stolen, stolen back, leaked to third parties who then spread their own disinformation-
The only prudent position the coalition could take, the only way through the confusion, was to demolish the hall of mirrors.
As it happens, they were right- and considering what could have happened to unsupervised chemical warheads floating around the middle east, just as well;
but yes, it would have set a damned ugly precedent if there had been nothing to find. It would have meant America had staged an all out invasion of a sovereign country, an ally less than two decades ago, on a fraudulent premise; an open act of naked aggression. Goodbye, moral high ground, the end of history is over; back in the Imperialist nineteenth century again.