> If you were born as male - you are male. If you were born as female

It's a tad more complicated than that, even at the biological level. Your sex is determined by your chromosomes, but for example, you can be born with chromosomes XXY. Which biological sex is XXY? Admittedly, this is an extremely rare occurrence. I guess you could argue that "presence of Y = male, absence of Y = female" to make it unambiguous.

There are peopel born with XY chromosomes that have functioning uteruses and ovaries. So its obviously not as simple as "There is a Y here."