I recently saw a good Frontline about this.
As I see it, the last time the U.S. had sufficient reason to attack Iraq was in 1998 when Saddam threw the UN inspection teams out. It is a too late to act on that. Iraq has, wisely, chosen not to invade any neighbors in the interim.
Iraq has not attacked the United States. Saddam is not massing troops on the border. There is strong evidence that the Iraqi government supports terror - but so do Saudi Arabia and Iran. Preempting an attack is a good thing. But can we go around “preempting” everyone who scares us?
This would be no War on Terrorism. Iraq is a nation. Don’t we have to declare war on Iraq to invade them? I know it is passe to actually declare war, but it seems like a prerequisite in this case.
Does the United States want to act with (at best) little international support? Most nations want to trade with Iraq, not invade it.
Might Saddam use weapons of mass destruction? In a survival situation why would he not use them? He is probably dead either way. Why not kill lots of Americans and be a “hero” in death? I understand that this apparent willingness to use WMDs can also be used as a justification to attack. But Iraq is hardly alone in pursuing WMDs or the willingness to use them. China is piling up offensive missiles near the South China Sea to threaten Taiwan - yet there are no U.S. invasion plans for China that I am aware of. Unless moving industrial production to China counts as an invasion, in which case the invasion is already underway.
Governance after any war may be the thorniest issue. A U.S. backed puppet government would probably not survive, in addition to being illegal* and immoral. I don’t think anyone can predict what might happen in the nation or region if we attack.
*International law is rarely clear but is pretty settled on wars of conquest.