I will say flat earthers have had some irrefutable arguments against the moon landing. Oddly enough I have personal experience that says they are right about another phenomenon. As a Mariner you can do a calculation to see what distance a light or structure (like a lighthouse) should become visible based on the height of the observer, the height of the object and the curvature of the earth. The curve of the earth with theoretically block your view of the object, until you are close enough. Assuming I have high visibility like no fog, smog, or rain, I have never had the horizon block my view of an object. This weirded me out when it happened time and time again, and I did the math myself plus checked with an online calculator. The official explanation is 'light refraction' bends the light over the horizon and allows you to see a mirage of the object; but I don't understand how refraction could work so consistently. Spooky stuff.