I think (for me) the killer response from the Prof Dave video was something I've mentioned before, but with nothing like Dave's eloquence and ability to cut to the heart of the matter. The flat earth model is fundamentally flawed.
Not only does it fail to predict what is observed, it is in contradiction to itself.
It can predict the daylight / nighttime cycle poorly, or it can predict the seasons incredibly badly. It can't do both at the same time. It's a garbage model.
Weirdly, reality (ie, the earth is a sphere orbiting the sun) covers both of these with simple elegance. Protesting otherwise is either willfully ignorant, stupid, dishonest or all of those at the same time.
