There were a few conservative realists who, to their credit, opposed the Vietnam War early on for practical, not ideological, reasons. Hans Morgenthau, the author of Politics Among Nations(1948), threw cold water on the notion promoted by the “best and the brightest” in Washington that the fate of Asia and the global balance of power was at stake in Vietnam:
If the stakes in Vietnam are as high as the supporters of the war make them out to be, if indeed the credibility of the United States and its prestige as a great power are at issue, if perhaps even the fate of Asia and of the non-Communist world at large will be decided in Vietnam, then the risk of a direct military confrontation with China and the Soviet Union is worth taking. If, on the other hand, the stakes are minor or as mythological as the commitment to a Saigon government and the eagerness of the people of South Vietnam to be defended by us have already proved to be, then the risks we have been taking have been out of all proportion to the interests involved.
Morgenthau acknowledged that we had placed our credibility at issue in Vietnam, but that didn’t mean our interests justified doing so, and prudent realism counseled cutting our losses before they got worse. Morgenthau wrote this in May 1966. The next month, Morgenthau criticized President Johnson and his national security team for “seeking a victory that cannot be obtained with the means employed” and for promoting the idea that increasing those means will allow us to “achieve the ever elusive end.” American policy, Morgenthau wrote in another article, “must be to avoid getting more deeply involved in [the war] and to extricate ourselves from it while minimizing our losses.” In short, for Morgenthau, there was no vital American interest at stake in Vietnam, therefore we shouldn’t waste our limited resources and American lives there.
In an essay in Foreign Affairs in 1967, Morgenthau wrote that the United States must be more selective in determining when and where it should directly intervene in military conflicts. He ridiculed the notion that America had the resources and the need to directly combat communist aggression everywhere in the world. “Intervene we must where our national interest requires it and where our power gives us a chance to succeed,” he explained. “The choice of these occasions,” he continued, “will be determined not by sweeping ideological commitments nor by blind reliance upon American power but by a careful calculation of the interests involved and the power available.” Something we failed to do in Vietnam.