> "Basically, you have people who could be cured of flat Eartherism by going out just one whole night and watching the stars rotate around the pole, just one trip to the ocean with binoculars to watch a ship disappear over the horizon, just one full day of measuring the shadows of the sun and doing trig, yet they refuse"

Somebody who's fucking with you would refuse to do this and instead laugh at you for being so naive as to not know binoculars have circular lenses, or some other nonsense excuse more creative than that. Refusal to engage in honest investigation of the truth doesn't prove somebody is unintelligent. Furthermore the incontrovertible existence of unintelligent people doesn't prove that flattists must be unintelligent people. It's very easy for a reasonably smart person to pretend to be very dumb because they consider it entertaining (or for other motivations.)

As for sincere expressions of anger, I've seen it more often from round-earthers than flat earthers. Phrases like "fucking dumbass YouTube videos" betray some strong emotion that I suspect (but cannot prove!) you aren't faking.

>But then again, what are you gonna do? I tell them to predict eclipses

Did you know the Babylonians could do this without a heliocentric model of the solar system? I suppose you could say that a working knowledge of EAE would be a demonstration of reasonable intelligence, but the lack of such knowledge could hardly be considered proof of lacking intelligence. Most intelligent people have never bothered to learn how to use Babylonian astronomy omens.