Well, you can see this problem from a different angle. That is, it all comes down to (1)weapon and (2) money. If we can deprive both to terrorists, we have a great head start. Yes, organization is still there which will be taken out one by one. But if money goes and weapon goes, they are so busy making ends meet that they may not have time for terrorism. To deprive (1), Iraq has to go because Iraq has many WMD to share with terrorists. To deprive (2), we encourage Russia to boost its oil production, lowering oil prices and bankrupting Saudi and other Gulf states. So Iraq is eminently relevant as well as Saudi.