That was true of Vietnam and South Korea too. And in Iraq we were toppling a brutal dictatorship and in Syria we would’ve been doing that. The U.S. shouldn’t have been getting involved in any of those. Democracy promotion is not a legitimate foreign policy—because for many countries (maybe most countries) authoritarianism is better than a dysfunctional democracy.

Once again, your argument is in favor of not helping the Allies against the Axis powers. This is not about democracy promotion. It's about repelling an invasion from a dictatorship. Invading a nonexpansionist Third Reich is a different proposition from helping other countries fight off an invasion from a Morgen die Welt conqueror. As I said, I agree the US shouldn't install and prop up illegitimate governments like the RVN. The people ruled by the illegitimate government won't appreciate it. That's not what's going on here.