I've been trying to pin down exactly what it is that makes some stuff feel like basically being realistic about how the world works, while other stuff feels inherently crackpot. Like, it's essentially some combination of how many people are involved and how outrageous the stuff that they're meant to be doing is.
For instance, you could kind-of peg Gramsci's theory of hegemony as a "conspiracy theory" because it's essentially about a whole class of people colluding to achieve something, but you wouldn't because it's basically an emergent property of a whole load of little bits of locally plausible, self-interested behavior. Whereas MK Ultra at the opposite end of the scale involved explicitly coordinated and obviously shady stuff, but the people doing the shady stuff were basically a relatively small number of operatives of the US Government's Department for Shady Stuff, so again, it doesn't feel that out there. Whereas when you work it through, proper crackpot stuff tends to need you to believe in a whole load of people having been strongarmed into doing stuff that's way outside what they'd normally do without anyone speaking up...