Cam Ranh Bay is the probably the best natural harbor in the region. Having access to it is in our interest, and it doesn’t compel us to do anything for Vietnam that doesn’t further our interest.
We don’t have to be the military guarantor of Vietnam in order to take advantage of the offer of access to the base. They are quite capable putting together an army for their own defense. What they have no experience in is a blue water navy. Let them spend the manpower and money to improve the port facilities. That’s their price for having us hang around and defend the sea lanes that we want open.
You make a consistent, logical case for your point of view. I’m not entirely convinced by it, but it is worthy of consideration.