Not to worry. After all, we stopped Iraq's extremely advanced nuclear program.
Saddam relocated his Chemical-Bio WMD program to Syria due to the huge amount of advance warning he had we were coming. And he relocated his nuclear program to Iran by a large number of accounts. Suddenly, Iran is on the verge of being a nuclear power. AG Khan was a Chinese puppet, and helped all the players. Fortunately we nabbed Libya's WMD in time. (You lefty's always forget that one)
As Gomer Pyle would remark, "Surprise, surprise, surprise!"
All and all, I guess your "common sense" lefty retort is neither legitimate nor sensible, albeit it is "common."
Saddam's weapons still lurk behind enemy borders. What are you going to do about it?