Irrespective of whether they had them or not - that's no reason to goto war. Granted perhaps the UN resolutions didn't specify what action would be taken, but its so typical that the US resorts to war to resolve things.

So if the Iraqis had so many weapons - how come no-one seems to know where they were.
I don't doubt that they have illegal weapons, but I doubt the sincerity of the US's cause.