I'd be very curious to know how many people actually believe that. I speculate that it's vanishing small. With these kind of "conspiracy theories" some people

I'd be very curious to know how many people actually believe that. I speculate that it's vanishing small. With these kind of "conspiracy theories" some people like to engage in the thought experiment, essentially thinking through what would have to be true for the conspiracy theory to hold. They adopt a position about it to engage in debate, sometimes as an intellectual exercise (even if a low brow one) and sometimes just to troll. I've got caught by such people before, that are really just being outrageous because they want attention, but at the end of the day they don't really believe it. Flat earth is the other classic example of this. Conspiracy theories are also the ultimate strawman, and it serves a lot of interests to promote the belief that lots of people believe in absurd conspiracy theories, and that those who disagree with anything mainstream almost certainly do so because they are stupid enough to believe in some outrageous conspiracy theory. Ironically, the idea that lots of people believe in conspiracy theories is in a sense a conspiracy theory in itself.