Are you sure there was a widespread conspiracy theory about a CIA mind control program before 1975?
idk, I wasn't alive before 1975. But even today, people will laugh at you if you say "MK Ultra" as though you're David Icke himself.

What is the difference between idiot theories and reasonable ones?
Literacy. Flat earth is an idiot theory because it makes no scientific sense. Same with 5G covid and shapeshifting lizards. Moon landing hoax, not so much, I mean, at least that's feasible, even if it's incredibly unlikely.

The difference between conspiracies and conspiracy theories is that the former has evidence to prove it.
So Einstein's Theory of Relativity has no evidence? I think you're misusing the word "theory", much like poop.