If we had stood our ground in Vietnam against communism we might not be where we are at today. Few people believe as you and I do, due to decades of propaganda.
The same folks killing commies in Vietnam will likely be killing them on their home soil.
We stood our ground in Vietnam; it was South Vietnam that couldn’t. In addition to a public relations problem (winning hearts and minds), they were doomed when leftists in Congress cut off their supplies (after we had already withdrawn). Units literally ran out of ammo.
Particularly if we had stood against it at home. Jane Fonda, John Kerry and many of their ilk should have been tried for treason.
Also the geography had us & South Vietnam continuously “outflanked” unlike Korea. Routes for reinforcement & supply through Laos & Cambodia made it a “war of attrition”. A “war of attrition” is something you don’t want to do in Asia. They will always spend more “bodies” then the West. In situations like that the West’s only choice is move the war to a new level - nuclear. Something we were not willing to do for a lot of reasons.