Both have made good points. I think that one's motives are always an important consideration.
I am thinking back to the American Revolution which in my opinion was a war that was worth fighting simply because the British were not treating the American colonists equally as the citizens of Britain. So, the American war of Independence was fought because of unreasonable expectations and heavy handed taxation. Could the situation have been resolved a different way? Probably not, as King George and the Parliament looked at the colonies as a cash cow to be exploited rather than as equal citizens with the same rights.
Moving forward a few years. WWII was fought after WWI because the peace ceded German territory to France as part of the restitution. Maybe WWII could have been avoided if the terms of the peace of WWI were more reasonable. But, up until WWII, wars had always been fought and settled by land acquisitions. WWII was necessary simply on a humanitarian front because of the reprehensible things that Hitler's SS and Nazis were doing to any who did not go along with the Third Reich.
I think that Viet Nam is a police action that wasted many lives and did not accomplish very much other than kill many on both sides. Aside from giving battle experience to soliders in "peacetime" , Viet Nam was not cost effective, did not accomplish the goal of keeping South Viet Nam free from communist rule, and wasted more lives than were "experienced" in battle.
I think Iraq is another Viet Nam. The profit motive is the cause of the war. No one has told the truth about Iraq from the beginning to right now. The truth is simply that the oil is worth fighting for and having control over as everything about American business and industry runs on oil. But, the run-up to the Iraq invasion and deposition of Saddam Hussein was to villify him (he was a bad man) and whip up a war fervor that would make the invasion acceptable to the American people. The jury is still out on Iraq, but I think in time, history will show that this was a war of greed rather than liberation.