Of course, we cannot re-run history to see how things would have turned out if we had done something else instead of what we actually did do. I do doubt, however, that there would have been much Iranian-Iraqi collusion, given the history and the animosities and rival ambitions there. And Sadam's chemical weapons probably represented next to no threat to CONUS.
The best argument for taking out Saddam's regime was that it was expedient to drive home the point, made with our initial Afghan intervention, that it is dangerous for Middle East governments to annoy us too much. If anybody was pre-destined to be the second object lesson in the perils of antagonizing the U.S., it was bound to be Saddam.