Hermaphroditism is incredibly in humans but it does happen.
L
Not someone with a birth defect but a true hermaphrodite that is fully fertile both ways.
You can't because no matter what they do, and believe me they have tried, the amount of hormones that are needed to make a fertile female result in the male reproductive system being rendered infertile and vise versa.
Intersex happens in mammals. Hermaphrodite does not.