The difference is that Vietnam was fighting against colonialism and to establish socialism, while Ukraine is being harvested for resources by the west and is used as a battering ram against geopolitical adversaries of the west, including by arming and empowering neo-Nazis against those in the Donbass region. This is just metaphysics, thinking you can take a very specific set of circumstances out of its necessary context and dogmatically apply it to every circumstance.
The difference is that Vietnam was fighting against colonialism and to establish socialism, while Ukraine is being harvested for resources by the west and is used as a battering ram against geopolitical adversaries of the west, including by arming and empowering neo-Nazis against those in the Donbass region. This is just metaphysics, thinking you can take a very specific set of circumstances out of its necessary context and dogmatically apply it to every circumstance.