Check comment# 28 on this thread about WMD in the Duelfer(sp?) report.
For example, if Sarin-tipped artillery shells had constituted the known sum of Saddam's WMD programs, they would not have represented a sufficient reason to go to war -- on their own. It was the suspected presence of a nuclear program and known biological weapon research that drove the decision.
And, to my mind, fully justifies it still.