One element of this theory is that western countries were sensitive to communist propaganda that the West was a hotbed of racism and colonialism. Throwing open the borders to Third World immigration was a way of refuting these claims. It’s notable that the United States, Britain and Australia all moved towards liberal immigration policies in the 1960s. These three countries all felt themselves to be particularly vulnerable to charges of racism and colonialism (Britain because of its imperialist past, the United States because of its imperialist present and Australia because of the White Australia Policy).
The move towards open borders was also a means of furthering western propaganda about the virtues of the Free World and also as a means of trying to cement various defence alliances in Asia, Africa and elsewhere.
There’s no question that “victory” in the Cold War came at a substantial price. The dangerous growth of the military-industrial complex (that President Eisenhower tried unavailingly to warn the US against) was one of the big costs. Is it possible that the foolish enthusiasm for open borders was another cost of the Cold War?
Of course this begs the crucial questions - was the Cold War necessary and was it worth the cost?
I think that while Stalin was still in power some kind of confrontational posture, or at least an aggressively defensive posture, probably was unavoidable. The Soviet Union under Stalin really was an Evil Empire and while Stalin’s foreign policy was often cautious there’s no doubt that his long-term intentions were pretty sinister. In the Khrushchev era the Soviet threat was still pretty real, this being as much as anything a product of Khrushchev’s unpredictability.
I’m not really sure that the Soviet Union under Brezhnev was quite such a mortal threat. The success of Detente in the 70s tends to indicate that a live and let live policy was quite feasible. I’m not suggesting that the Soviet system under Brezhnev was either admirable or benign (far from it) but much of the anti-Soviet hysteria was overblown.
In any case whether the Cold War really was or was not a confrontation between good and evil isn’t really the point. The point is that the Cold War caused a substantial deformation in western foreign policy, and perhaps domestic policy as well, and we may be still paying the price.
Of course what all this means is that we should be incredibly careful about being drawn into another Cold War with either Russia or China. The West has its own problems to solve and a Cold War 2.0 may well make it impossible for us to confront our very real current problems. We need to be particularly careful about falling prey to the Law of Unintended Consequences.