I won't parse my words. Both you and your mom drank the koolaid of your respective beliefs.
The war's really about a dictator that played a shell game with the most powerful country in the world at a time it got sneak attacked and the rebuilding that ensued.
Tell your mom wars happen all the time, and how the difference between a war and a fistfight on the street is that a fistfight involves individuals while wars involve societies so there's nothing new under the sun.
And tell yourself "If we let this dictator live, we'd be fighting both Saddam and Osama together instead of separately" because that's what the war was really about, stopping Saddam Hussein and OBL from joining forces.