Eric:
The Vietnamese War IMHO:
1-Demoralized our population, making it more difficult to intervene against communist aggression where necessary (e.g. Central America).
2-Ruined our reputation with allies, becuase we turned tail and abandoned the South Vietnamese.
3-Ruined our international reputation, because of all the negative press (baby killers, etc.)
4-Along with the Great Society, produced stagflation that made capitalism less attractive, both in our own country and abroad.
5-Completed the radicalization of the media and academia, as well as much of the population, at home.
6-Virtually destroyed the morale of the U.S. Army.
7-Limited the funds available for our other defense needs.
If you look at our situation in 1979, it was not looking too good. Politically and economically the commies and Arabs had us on the ropes. Our influence was in decline everywhere.
A good book to read on the collapse of the West in the late 1970s is "How Democracies Perish" by Jean Francois-Revel. He argues pretty convincingly that the only thing that saved the West was the Sino-Soviet split. Essentially, the West was saved by the competition between two totolitarian powers.
Reagan was eventually able to get things turned around, but without him I think we would have been sunk. But maybe our collapse in Vietnam was the shock we needed to elect a right-thinking guy like Reagan!
I am not saying we should have let the NLF take the South in 1963. But if we were going to fight, we needed a strategy that would lead to victory. The strategy we had in Vietnam killed lots of people, but would never lead to the achievement of our goals.