You want me to explain why Vietnam made different choices than Korea using my vast understanding of Vietnamese politics and their distinct perspective on US military strategy?

What beliefs do you think I am trying to justify despite facts, exactly?

That Vietnam, Laos, and Cambodia might, in the future, become victims of overt US military action? What facts, exactly, do you believe completely eliminates this possibility? Why do you think I am trying to cherry pick facts to justify something as simple as countries that were attacked once might be attacked again? Exactly how many facts are needed to support such a simple and non-controversial conjecture?

Each nation makes choices based on their ruling class's understanding of the world, how it works, and their understanding of their own place in that world and their objectives. I don't know exactly which differences in these things led to Korea developing ICBMs while Vietnam did not. Perhaps it was merely physical proximity to the USSR, perhaps it was a specific understanding of their respective geostrategic locations, perhaps it was the result of their respective wars with the USA. I have not done a multi-decade comparative analysis of the native publications of the Vietnamese leadership and Korean leadership to answer your question.

What I am aware of is the history of US military interventions in the region, contemporary US military actions, and the current trends of geopolitics. This leads me to the very lightly held simple conclusion that the US could deploy military assets to the region and in fact take military actions if it determines it would serve a purpose.

Your position is that this is literally impossible. My position is merely that it is possible, not that it's inevitable. I would propose that your postion is the one that require extraordinary evidence to support, and I would welcome such a well researched and peer reviewed set of papers about the literal impossibility of future US military intervention in Vietnam.