Equally the US has not sided with the Afghan government against the Taliban (at least not since Mr. Trump became the Commander-in-Chief and discovered that the US had bought into a war that it simply could not win because (to stretch a point) in Afghanistan "stranger" and "enemy" have much the same meaning to the average Afghan.
The difference between the Kurds and the Vietnamese is that the Vietnamese were fighting to recover the independence which the Vietnamese had obtained from their colonial masters (France) and which the US government had assisted the French government in quashing while the Kurds have NEVER had an independent national existence. I am sure that you are aware that the US government stands firmly on the position that
NO group has the right to independence from an existing national body UNLESS the US government doesn't like the existing national body, in which case NO existing national body has any right to refuse to allow any group which says it wants independence from it that independence.