Living in Canada at the time, a veteran of WW2, I had a number of young Americans sleeping for a few nights in my basement, on their way to making their decision. Everyone was engaged in soul-searching. Often wondered what happened to these young men of concience. I know some went back, and some stayed in Canada and made good here; I do know about them. All of them were serious, and well-educated.
No one in government seemed to have the historical sense to see that the Vietnamese, after fighting the French to a standstill, were nationalists first and communists second. By abandoning the war (undeclared or not), union was finally achieved; and we were not faced with another situation like Korea where the confrontation drags on (I think both the Chinese and Americans realize now that they created a monster). Many thousands on both sides lost their lives as a result of the Vietnam war, I believe needlessly.
Another generation must pass before the war can be assessed rationally.