By the time of Vietnam, there was no MacArthur. Certainly respectable conservatives did not bring up any embarrassing questions. At first, Reagan said we should either fight or get out. But once Kennedy and Johnson dipped the flag in blood and then ran it up the pole, all the conservatives saluted and backed the war. That is happening now, again.
Respectable conservatives have exactly the same contempt for the Constitution that liberals do.
Americans were dying by the thousands in Vietnam, but that didn't mean the country was committed to anything. It is also his idea of constitutional government. This is the key to the whole mentality of respectable conservatism. Respectable conservatives have one, and only one, real concern in life. That is their respectability.