NIMH is likely to happen still so they will switch to that overpopulation theory.
Uh...
I don't think you're entirely plugged into what I'm talking about here.
See, there was concern over the Earth's ability to feed people being overrun by overpopulation in the '50s and '60s,
and this was founded in fact, though admittedly in ignorance of the sheer high yields possible in theory with high-input Green Revolution agriculture.
"Overpopulation" is not some kind of bullshit 'theory' in the full general case. It's a valid concern that can apply to real societies if there is a reason for the population to not be able to sustainably expand. It's sort of like how 'global cooling' isn't a problem we're worried about right now, but it's definitely a problem that would loom very large if we actually fought a major war and touched off nuclear winter. There's a difference between a problem you don't have and a problem that isn't real. Moreover, there is the observation that to some extent we
don't have an overpopulation trend because many of the trends being observed in the 1950s and early 1960s (such as the baby boom) were not followed indefinitely... but it could not be rationally predicted that this would be a non-issue.
...
Now, I'm not entirely sure what you mean by NIMH. Do you mean the 'rat utopia' experiment? If so, yes; that did become a sort of trite and trivialized example used in 60s and 70s social science to support the idea that overcrowding can potentially cause serious problems among rats and, implicitly because it was 60s psychiatry and behavioral science and all that, among humans. But I don't think that it was "switched to" as an "overpopulation theory," so much as it was part of a broader trend to recognize that the Earth's resources are not literally infinite and can be exhausted by a large enough human population that exploits them greedily enough.
Which is, uh... true. Even if some people got the math wrong or made incorrect predictions because they didn't specifically allow for this or that technology, it's still objectively true that the planet's resources are finite.