"I think it's clear that there were basically five types of people who opposed the Vietnam war:

1) Isolationists of the "this is none of our business" variety.

2) People who just didn't want themselves or their brothers, husbands, and sons drafted.

3) Liberals who thought it was a lost, doomed cause.

4) Pacifists of the "all war is bad" variety.

5) Communists, communist apologists, and generally anti-American dips***s.

The only people I really hold in contempt are groups 4 and 5. Pacifism is immoral, selfish, and destructive. Communism is as evil as Nazism. But the others are people I can understand and respect."
http://www.deanesmay.com/posts/1114787007.shtml

It's an interesting and the comments are worth reading.
I've been thinking about isolationism/pacifism lately. There was few speakers on stage which televised by CSPAN. None of them seemed very remarkable, one was foaming Lefty who managed to get large cheers from the audience, though to her credit she didn't lose it when a Iraqi vet from audience refuted most of what what she was saying.
Anyways a couple of the somewhat Neocon speakers were talking about need for war only exceptional circumstances, and later asked the one Latino speaker what the US policy should be toward Latin American should be. And this speaker said something like "just leave us alone" [which got some cheers from audience]. And then proceeded to argue against the Haiti intervention [which he labeled as American Leftist intervention] and said he was just as much against this as other American intervention.

The thing is that America was founded on principles which argued for isolationism- what was the war for independence from Britian but a reflection of isolationism? And concept of Federalism also involves a form of isolationism. And up until WWII this country had a strong tradition of isolationism.

Now the argument against isolationism is that we living in a smaller world, a more connected world, and globalization.
I think the idea of isolationist tradition has been used as club against Free Trade, whereas their isn't any reason why you couldn't have a stong federalism type system and strong Free Trade.

The problem is the US has morphed into a strong central govt, and we are "subconsciously" reflecting this "value" onto the world.

The main argument against isolationism is that war will start somewhere and grow into a large war which will evenually force us to intervene. Or worse, it will turn into nuclear war. I think the formation of the EU weakens this argument and I think that other mechanisms- for more effective uses of soft power- and an effective UN. For instance Sudan could be resolved through soft power- but of course it's not happenning.

Oh, I guess I'm rambling, sum up and end this: in the context of Cold War, isolationism and pacificism were mostly about avoiding the issue of USSR's threat to world peace but in today's climate aspects of these concepts have more merit.