I'm afraid the justification for war isn't that simple.

There are numerous other dictators in the world, and some even supported by the US.
Ok, let's admit Saddam is the most even one of all.
How come he was an ally 20 years ago? At that time, he already was a ruthless dictator, killing his opposition.
But then, he invaded another country and there was worldwide support to get him out of Kuwait.

The problem is: what happens next?

While the US has never been invaded in its history and enjoys the security of being on an island (a very big one) tens of thousands of miles away from the Middle East, it pretends being threatened by Saddam.
If Saddam is removed, I'll bet you there's 99,99% chance that there won't be any democracy in Iraq. The US has never been able to introduce, by force, democracy in a country that had never known it before. Neither have the old european colonial countries, btw.
That's the main problem: the Iraqi people; what do they expect from the US and what will they get?
I'm sorry, but to force "our way of defining freedom" into them will in no way be considered freedom to them.

The best freedom is fought for, not forced upon.

A war might help in the very short term, but not in the long one.

Raoul