That definition of “normal” is irrelevant to the biological effects of mutation on fertility.
Here: If the human reproductive system has evolved over millions of years in a condition where the vast majority of the population are one of either two sexes, with particular chromosomes even being present in only one of the sexes, then a mutant that somehow ends up with both sexual organs is almost certainly going to having all sorts of problems fertility-wise. That kind of mutation breaks the assumptions the reproductive systems have evolved under (assumptions such as amounts of testosterone/oestrogen/whatever other hormones in the blood, the physical arrangement of the sex organs, and probably all kinds of other stuff).
That definition of “normal” is irrelevant to the biological effects of mutation on fertility.
Here: If the human reproductive system has evolved over millions of years in a condition where the vast majority of the population are one of either two sexes, with particular chromosomes even being present in only one of the sexes, then a mutant that somehow ends up with both sexual organs is almost certainly going to having all sorts of problems fertility-wise. That kind of mutation breaks the assumptions the reproductive systems have evolved under (assumptions such as amounts of testosterone/oestrogen/whatever other hormones in the blood, the physical arrangement of the sex organs, and probably all kinds of other stuff).