I am a 72 year old vet of the war. I remember it well. The war should of never occurred, but the times dictated our involvement. The domino theory was looked upon very seriously at the time. China had gone to the Communist side and the threat of losing all of Southeast Asia was ever present then. One thing that has not been mentioned and is very factuql, is that although the war was a mistake, we had it actually won after the Tet offensive by The North Vietnamese. We demolished their army to the point that General Giap their commander was ready to sue for peace, but saw the demonstrations and knew that would sway the war their way. He actually looked at the demonstrators as being a fifth column. The press and specifically Walter Cronkite reported as though Tet was a defeat, but it was quite the opposite. The war as I said was a waste of many good soldiers, marines, and airmen.
There was no "winning" a war in Korea or Vietnam just the same as their is no winning a war in the Middle East.
People are stuck in 1945.
We were the country that won WWI and WWII, but those were wars that 1) Had VERY clear moral rationales 2) Involved major industrialized countries.
Every war we have bumbled into since WWII has had murky, geopolitical rationales. I get the thinking about the dominoes and probably would have seen that as a viable argument at the time.
But, end of the day, when you need to debate if you should be in a war, you shouldn't be in it. Just based on the actual threat level that justifies the action, but also relative to, in this day and age, in a democracy, it isn't just conquering counties by regimes, it requires the support of the public.
This "we lost because people back home didn't mindlessly, endlessly support sending our 20 year old boys into a meatgrinder for a country that posed no threat or had no loyalty to us" mindset is oblivious to the fact that we are, in fact a democracy, that we collectively have a voice in these matters.
You also can't "win" wars in these piss ant, third world countries because they don't just put the flag up and go about the business of rebuilding their country to get back to a civilized way of life like Germany and Japan did.
They had nothing, live in jungles or deserts and just crawl into their woodwork and engage in guerilla warfare (Which, not for nothing is pretty much how we got our independence).
Additional to this point - end of the day, the people of Germany and Japan accepted that they were wrong, it was pretty clear what they did, and they did some epicly horrible things, so the conceded.
We went over there, they were mostly minding their own business and we blew the $hit out of their country. They didn't do anything wrong for us to be there in the first place.
Why we have to keep learning this lesson is beyond me ...