I thought of that before you posted your reply. We did extensive psy-op work in Iraq before the invasion making the point that any commander who used chem or bio weapons would meet a bad end. That may have had an effect. But I still can't see at least some of those die hard Baathist or "Fedeyeen" types not using them at least once.
I think the reason Iraq would not have given WMD's to AQ or other such types before the war is that he valued his life and regime. And surely if we had such info that he did we would have made it public. Chem and Bio weapons have "signatures" once used and can be traced. Sadaam was just like Stalin- a murderous madman. And just like Stalin he loved his power and wanted to stay alive. I don't see Sadaam giving WMD to extremists like Osama in peacetime. But - with nothing to lose and America about to invade- why not give WMD to whomever? I don't think we are safer. Maybe - if Iraq does indeed become a stable Democratic regime and example of prosperity to the rest of the Middle East and thus cause revolutions then we will be ultimatley secure. But I Don't see that security for 5 to 10 years.
The argument to the contrary is no different in principle from the arguments against taking action against the Taliban prior to 9/11, with the only difference being that Iraq under Saddam was far more dangerous than the Taliban on its worst day. We should have learned our lesson the first time around.