I am the greatest...

Martina Navratilova has raised a question that I posted about a couple of months ago.  Now that - it appears - we have the right to determine for ourselves what gender we really are, what's to stop a hitherto somewhat mediocre sportsman deciding that he's really a woman, and then competing against women and, thanks to his masculine physiology, sweeping all before him/her?  Press "sisters" anyone?