Those are all also false, depending on the perspective. Flat from where, to whom. Cancer in who, and how many, after how long, from which ratios, with which error rate on which factor. Global warming to who, where, and which men.

(I'll offer that these may be maddening perspectives, but that does not itself mean they are invalid)

If you want to reconcile or come to a shared understanding with flat-earthers, it may help to meet them where they are at, and show them why their mental models are effective and truth-yielding in some ways, while also limited in others. It may also help to understand their psychology, and work from a different angle. Wielding "wrong" as one's only tool can limit the opportunity to try a variety of such approaches, and test for effect.

Absolute truth is a mental model. It may have its uses, but its own absolute utility or validity is not guaranteed. Further it may do one great intellectual or psychological harm to remain caught in this logical trap: It feels so right, but its key doesn't fit all these locks (others' annoying positions). So why keep using it over and over? Humans can be amazingly flexible thinkers, holding contradicting mental models in the same mind. So why not take advantage of this? Absolutes and fixed thinking are a huge liability in this way.

Edited to add: In most cases the stakes are lower, too. Global warming probably won't be solved by one person's mental models, no matter how absolute or flexible and thoughtful. So there's also a misleading aspect, perhaps a falsehood-perspective, to the given examples. See also: Was so-and-so the dictator good in some ways, or pure evil, etc. These questions may belie the hyperbolic beginner mind more than they form a high-quality test of the framework.