I often hear people say things similar to “In 200 years, when they dig our bones up, there will only be men and women” as a way to discredit nonbinary people. I think statements like this have a fundamental misunderstanding of the difference between sex and gender.
For most of our history, the two have been pretty intertwined. But the core difference is that sex is biological and static (XX vs. XY chromosomes), while gender is societal and fluid (man, woman, boy, girl, nonbinary, etc.), and the two don’t have to be linked.
The idea of having to be a man or woman as your only two options is silly to me, as the concepts are so abstract that they mean different things to different people all over the world, so at that point why even limit it to just two? So if someone is nonbinary, sure, they are going to be biologically male or female on their medical sheet, but in society there is no reason for them to have to fit into the boxes of being a man or a woman.
At the end of the day, I don’t see why we can’t just call people what they want to be called.