Unless you are seeing Vietnam in the context of the Cold War [a front in a war], Vietnam was relative to our present war against Islamic fascist rather insignificant.
It's true we lost more troops in Vietnam, though we have already lost more innocent American civilians than compared to the Vietnam war. But we should keep in mind that this war against terror, has barely begun. And most Americans don't even know we actually in a war.
Now, it's possible things will unexpectedly change. E.g. Iran may change course. Or significantly more Muslims might fight effectively against this disease. But there is not much hope for this.

But, if such an insignificant war as Vietnam works as an excuse, then one expect many more such potential excuses in the future.
I would say Apollo was similar Gulf war I, Bush senior achieved his objectives- continuing on to completely defeat Saddam could and probably would mar the achievement. Though the result that followed was that 100,000's of Iraqis died from Saddam's effort to maintain control. The purpose of Gulf war I was to kick Saddam out of Kuwait. The purpose of Apollo was to beat the Soviets in the space PR arena.

But I agree that Apollo died because of politics. But Apollo was born from politics. NASA exist today in present form because of politics.
What I said: "they stopped Apollo is they were afraid crew would die." Is all about politics.
Far more people died in coal mining than from Space exploration- that doesn't even begin the thought that coal mining should be stopped. And about 40,000 people die from car accidents each year- which an improvement from past decades.
And the other thing I said: "Lack of public interest & and public losing interest" is obviously all about politics.

NASA could kill hundreds of crew per year, if what they were doing was worth these deaths. Actually opening the space frontier is "worth" tens of thousands of death per year. But continuing the Apollo program wasn't "worth" 3.