Oops, I've noticed that Slate is not copy-editing these pieces before posting them. Better run that damn spell check before I send this one off!
We seem to now have settled into one of the great old Cold War debates--was limited containment (of Western Europe and Japan) enough or did we have to worry about the rest of the world? The argument for limited containment, articulated best by Walter Lippmann and George Kennan, was that only the key centers of power mattered, so Europe and Japan were vital and the periphery unimportant. Keep the Soviets at bay at the core and you will succeed.
In general I have great sympathy for the Lippmann-Kennan view, have written nice things about both of them, and share their suspicion of the tendency to brand every molehill and mountain around the world a vital national interest of the United States. To some extent Acheson shared this approach. He was unabashedly Euro-centric, thought it was silly to spend time courting countries like India and Egypt with aid, opposed John Foster Dulles' "pactomania" (signing up countries into pro-American alliances). On the single most important core-versus-periphery issue of his tenure, China, Acheson was decidedly realistic. He thought China was going to go communist, that there was little the United States could do to stop this from happening and that it was not a mortal blow to containment. His policy was, he explained, to "let the dust settle." Now this is just the sort of masterly inaction that you seem to commend. (Of course it consigned the Chinese people to years of oppression, famine, and political murder--with tens of millions dead at the end of it all.)
With regard to Vietnam he did, like almost every other Cold warrior, believe that the United States could not abandon the government of South Vietnam to the mercy of a brutal communist dictatorship. He exaggerated the importance of Vietnam, but he changed his mind by 1967-68 and then advocated immediate disengagement. (When the senior military officer briefing Acheson at the White House explained that victory, in the "classic" sense of the word, was not the US military's goal in Vietnam, Acheson archly responded, "Then what in the name of God are 500,000 men out there doing--chasing girls!")
But you're right to note that in some other cases--mostly when out of office and getting on in years--he was a superhawk. My explanation for this is that Acheson thought like a statesman not an intellectual. Thus distinctions like those between core and peripheral interests, while perfectly sound in theory, begin to crumble when, say, North Korea invades South Korea or the Soviet Union invades Afghanistan. It is fine for Kennan and Lippmann to say, "the balance of power will eventually work all this out," but the statesman does not have this luxury. The United States must have a policy that addresses the realities of the world as and when they happen. Again, I admire the Kennan-Lippmann position, but I do recognize that in the real world it's difficult for the world major power to follow the maxim--"don't just do something, stand there!"
Imagine a world in which the United States resolutely had not responded to any Soviet expansion outside of Western Europe and Japan. South Korea would have become a communist part of the north, Vietnam would have fallen in the early 1960s, South east Asia would have been threatened by communist insurgencies, countries like Egypt, Indonesia, Brazil, India would have titled (or titled further) toward the Soviet Union. In this context, do you really think that the Cold War would have ended when it did as it did? Do you really believe that "I Love Lucy" and Miles Davis would have done it all and we didn't need the Marshall Plan and NATO and foreign aid and the pro-democracy and pro-market programs of the U.S. government? That the virtues of Madonna and Coca-Cola would have won over the world and indeed to the Soviet regime itself? (The Soviets, for one, do talk about the importance of the Strategic Defense Initiative as convincing them that they were falling behind?) If you do then you have a greater faith in the power of free markets and popular culture than I do--and you should really be worried about Seinfeld, since you hate him. Me, I think he's pretty funny--and utterly inconsequential (the new opiate of the masses?) Power matters, Eric, not stand-up comedy.