the logic
The nationality of the terrorists on those planes is immaterial. How difficult would it have been to replace the Saudis with Iraqis or Syrians or Jordanians.
The problem we face is with the Arab world in total and specifically the powerful radical influence in all of their nations. Those radical elements have declared war on us just as Germany did. The choice of Iraq is no different than the choice of France or Italy as a place to begin the war against Germany on their own turf.
Events in history are unique and my comparison with WWII is an overgeneralization but no more so than your comparing us to Nazis and a helluva lot less offensive.