It's easier to justify this kind of madness when "most of these people are going to die when the nukes hit anyway." There really were a lot of people thinking that way. "These people are already dead."
To get a sense of the mindset here's a good profile of Herman Kahn whose research helped name a death metal band (Megadeth):
https://www.newyorker.com/magazine/2005/06/27/fat-man
"How many megadeaths (millions of deaths) will we absorb vs. the Soviets?" etc. A lot of this hideous research was to try to characterize the effects of a thermonuclear war and its aftermath to answer questions like that. The Soviets were doing similar things.
This I'm sure contributed to an environment where unethical research was tolerated and rationalized for other reasons too.
The 'bomber gap' and the 'missile gap' were fictions, with U-2 photo-intelligence showing the Soviets didn't have the capability to carry off a massive attack.
US politicians decided it was better to keep knowledge of the U-2 away from the US public - even though the Soviets knew about the U-2 starting on the first flight. The US even lied about the Powers U-2 crash in 1960, calling it a high-altitude research flight, with the possibility of an incapacitated pilot.
So I don't think it's right to say simply they believed the possibility, as that belief was deliberately inculcated by people who wanted a war, wanted increased war funding (the "military-industrial complex"), and/or wanted to leverage public fears for personal and political power.
It seems completely unhinged today, but this was right after the world had just been rocked by two successive bloodbath world wars. It wasn't that crazy in the 1950s and 1960s to think WWIII would be up in short order.
Another major factor was how much secrecy there was on both sides. Secrecy breeds conspiracy theories and paranoia. The Soviets were also preparing for a first strike from us and probably were following similar lines of reasoning.
I think Curtis LeMay - one of those in your category - was unhinged already. I think he wanted a war. This is the guy quoted as "Well, maybe if we do this overflight right, we can get World War III started". He wanted to bomb and invade Cuba, and do even more bombing of North Vietnam, and he wanted the US to get rid of its "phobia" about using nuclear weapons.
That's someone who wants war, and will manufacture an interpretation that justifies having that war. That's far different than simply drawing that conclusion from negative data.
Again, yes, I agree with your "it wasn't that crazy" part. My point is that many of the people who believe that were deliberately lied to, to encourage spreading that belief. While connected with secrecy, as you say, it was a deliberate conspiracy carried out in part to support what Eisenhower termed the "military-industrial complex."
Another thing that many are surprised by is how fashionable eugenics and forced sterilization were at one point in the US.
“I cannot read this sign, by what right have I children?” https://en.m.wikipedia.org/wiki/File:Eugenics_supporters_hol...
If it's unclear, I'm not defending or supporting any of this insanity, but emphasizing that the motivations were in no way racist. In general, if you want to learn more about the selection process for the various sociopathic experiments "we've" carried out through the years, the Wiki on MKUltra provides quite a lot of insight. [3]
[1] - https://en.wikipedia.org/wiki/Demographics_of_San_Francisco
[2] - https://pubmed.ncbi.nlm.nih.gov/28004553/
[3] - https://en.wikipedia.org/wiki/MKUltra#Experiments_on_America...
I think really the point can be most boiled down that even if everybody was all the same race, those sprayings still would've happened. And, in fact, it did happen in many areas that were mostly white. The case in San Francisco was even worse. Instead of spraying people with chemicals, believed to be safe, they were spraying them with live bacteria - which near immediately caused numerous health effects. So by focusing on race, you ultimately end up ignoring the real underlying issue.
[1] - https://www.vintag.es/2017/03/46-rare-color-photos-document-...
[2] - https://en.wikipedia.org/wiki/Pruitt%E2%80%93Igoe#/media/Fil...
Apart from the whole "purposely only testing people having a specific skin colour" thing.
Gee, that doesn't sound racist at all. :p
/s