I have been a bit of an activist on human rights in Pakistan and in the US, but before it started, I was never able to bring myself to say I was against a war in/on Iraq. Not that I was for it either. Governments go to war or interfere in other countries for national and personal interests--never for morals or ethics—or rarely so. My own country's record in Afghanistan is a wonderful case study. We stood up to the Soviets, which was good for all. But the way the governmet and the military went about it was, well, pretty objectionable. And that was back when there was a black and a white in this world.
One rather odd fact Americans need to think about is this: The only time Saddam actually used weapons of mass destruction is when he was a US ally. When he wasn't, he didn't. Which did not make him any less of a monster.
Why did the US go after him? Well, he wasn't "our SOB" any more. Which, from the strictly logical point of view of a nation-state or government, is a valid reason for going to war. Always has been, however much us 21st century liberals might think otherwise.
As for whether we did Iraqi's a favor getting rid of him—we certainly didn't do them a disfavor. But that's not the same as saying we did them a favor. We use a lot of playground analogies in the US. Here's one that might help in this situation: Say you are the little kid on a playground being terrorised by a bully. And there's a bigger person standing behind that bully handing him Gatorade, holding his towel and sharing the lunch money the bully just snatched from you. And then, suddenly the other, bigger person whacks the bully, and turns to you, cracks into a big smile and says in a very LOUD voice "Now on things are going to be all nice in this here playground." How would you react? That was the state of mind of Iraqis and a lot of the Muslim world the day the statue fell in Baghdad.