The world's governments, militaries, media, schools and literally everyone else except flat earthers claim with conviction and whole-heartedly believe that the South Pole is the Southernmost extent of their globe.
And by definition this must be the case because to continue traveling Southwards beyond this Southernmost point is tantamount to traveling Northwards.
If the Earth is not a globe, however, and is actually an extended level plane as claimed by flat earthers, continuing to travel South of the South Pole would not and could not bring the traveler back North; on a flat earth, the traveler would instead continue Southwards into unknown Southern territories that don't exist on a globe.
If NASA, the world's governments, militaries, media, academia and/or anyone else involved in maintaining the legitimacy of the globe concept truly wanted to shut up flat earthers once and for all, this is how easy it would be.
Allow for independent travel South of the South Pole, or livestream a full South to North circumnavigation of the supposed globe starting in Antarctica and traveling South.
Show the world's flat earthers that traveling South of the South Pole will somehow bring you North.
Whether you believe the Earth to be flat, globular, hollow, concave or otherwise, the freedom to independently travel and explore the Earth, from the North Pole to whatever exists South of the South Pole, to any and everywhere else, should be a fundamental and unalienable right.
Military vessels near the North Pole and Antarctica have repeatedly barred independent teams of explorers from traveling into these heavily patrolled and restricted waters.
The Antarctic Treaty prevents all independent travel South of the 60th degree South latitude, where rebels like Yarle Andehoy and his team have been repeatedly turned around at gunpoint, jailed and fined for daring to attempt.
What is so important in Antarctica that 53 of the most powerful countries in the world have agreed to patrol and enforce harsh restrictions and penalties on anyone who attempts to independently explore it?
Why has the entire continent of Antarctica and everywhere else on Earth below the 60th South parallel been caged off from us?
The only way we can experience Antarctica is by being a government employee and working at one of their bases, or doing one of their overpriced penguin tours along the Antarctic coast.
No one, even these very few humans, is granted the freedom to explore the continent, so even they are clueless as to what may exist at the furthest Southern extents of the Earth.