The remark about oil in the China Sea was often cited and not just by liberals Interestingly enough It remains a matter of disputres between China and Vietnam, although neither has had the resources to explore for what is there. I also heard it from the lips of priest who an old fan of Father Coughlan There was and is an isolationanist element in conservatism. You may recall that Bob Taft was not fond of NATO, and one reason Eisenhower ran for president was to keep Taft from becoming president. (His view of McArthur was also a factor). But this was a minor part of the argument that the domino theory was simply a ploy to maintain capitalist control over Southeast Asia.
It's new to me. There is definitely oil there, but the war in Vietnam was not fought over oil. Father Coughlin is not a good source. I'm glad Ike ran rather than MacArthur. Sounds like a lot to tin foil conspiracy nut theories to me.