>Yes but a flat-earther is a useful idiot for precisely zero dangerous social movements.

Incorrect. As with most if not all conspiracy theories, flat-earthism incorporates anger at "the establishment" because "the establishment" is hiding the truth. And this is the hook. If you can be convinced that a secret cabal is manipulating all science, controlling all governments, censoring all media and filtering all information in order to keep the basic nature of reality hidden from humanity - which flat earthers do believe - then you're susceptible to someone suggesting who that cabal might be. You know who.

True. I was being hyperbolic, but I hoped it was clear that I meant that flat-earthers are nowhere near the threat-level of something like a qanon or antivax movement, who are far more politically-activated, willing to take matters into their own hands, and likely to incite actual physical harm through ideological-driven behavior.