American culture, and I'm generalising, there are a million sub cultures obviously... Emphasises the individual. The American dream of you working hard to get some payoff, is an example. As such there is a lot of cultural pressure to not correct people when you are in conversation, it's more polite and acceptable to play along. Their stupid ideas, their problem.

And that's where Americans (again I'm generalising) are weakest here. Because stupid ideas are everybody's problem. Because once people go off-the-deep-end there is no easy way of getting them back. And a large amount of people involved in conspiracy fantasy is legitimising it.

So no Americans are not more prone to conspiracy fantasy, but American culture does permit fast growth of ideas. MLMs are another example of this. You can use cultural taboos and cultural elements to sell bullshit.