Opposition to the Iraqi invasion doesn’t necessarily translate into support for Saddam. One may actively support him or oppose him. One may actively undermine him in other ways, or merely contain him as before. The Saddamite slur is a form of intellectual bullying that attempts to bludgeon one’s opponent into acquiescence.
I’m not disputing that the cause was right, if the “cause” was the freeing of the Iraqi people from Saddam. But that was tacked on just before the invasion as a PR sop, after Bush and Blair had spent months on alarmist talk of WMDs, threats to peace and the like.
By US interests I mean geo-political and economic interests. The US is number one super-power, and if it wishes to remain so, as I assume it does, it needs to reduce any threats to that power. One perceived threat is the Islamic Middle East, so it needs to be “pacified”, by ensuring complaint regimes and the like. It is in US interests to have friendly and influential states in the region, so in that sense a successful invasion of Iraq would be the US interest.
The US also has economic investments around the globe. These need to be protected. In the case of my country, New Zealand, we are a law-abiding democracy, so American investors have few worries. But other parts of the world are unstable or actively hostile to the US, so a military presence and/or compliant regime is needed.
It’s difficult to pick one’s way morally through these entanglements, but one thing I do know: Iraq 2003 was not Germany 1939.