Fun background - a delegation from "French Indochina" attended the Paris Peace accords in 1919 and petitioned Wilson, Clemenceau and Lloyd George for independence from French colonial rule. They were ignored.
In attendance with the Vietnamese delegation was 28 year-old Ho Chi Minh.
Missed opportunities and paths not taken, eh?
We always tell Liberals who cry about the founding fathers & slavery that they need to place themselves in the context of the times.
Likewise, when "judging" a war like Viet Nam, we must go back to those times.
May 1961, A MERE 16 YEARS after the end of WWII, JFK authorized sending an additional 500 Special Forces troops and military advisors to Viet Nam. Communism and the spread of it was serious. We had also ended the Korea conflict in the form of a cease fire and a split country, which was not an ideal outcome, but the spread of the North was still stopped.
In light of that we probably sought a repeat, another blunting on the spread of a norther communist country into another south.
Again, in the context of the time, that is perfectly justified.
Regarding your mention of Missed opportunities and paths not taken: I am sure there were missed opportunities just as there were before WWII. As for paths not taken, hindsight sure is nice.
But still, at the time, the action was justified.