For centuries, sports has always featured men competing against men and with the advent of women's sports, women competing against women.  Why?  Simply because all of us know that, physically, women cannot compete on even terms with men!  Men are simply built to be bigger, stronger and faster than women.  This is not rocket science but it is in fact, science.  Therefore, a man who believes he is a woman or wants to be a woman, will still perform like a man when pitted against a woman in sport.  Unless there is a surgery that will take away some of his bone mass, his muscle mass, his lung capacity, etc.., this wannabe girlman will have a huge physical advantage over virtually any woman.

So why should a women who has trained hard for many years to excel at her sport suddenly be faced with an opponent who she can't possibly beat just because that opponent was born a man, has the body of a man, performs like a man but wants to be a girl.  Why would we rule in favor of penalizing all female athletes just so a very few guys who think they are girls can put on a girl's uniform and go out and win almost every event, every time, and in the meantime, strip the female athlete of any possibility of fulfilling her dream of being the best or winning a medal?  Something that she may have devoted much of her life to.  We must protect women in sports by forbidding anyone other than a biological woman to compete in women's sports.

This also solves the issue of female athletes having to suffer the stress and embarrassment of suddenly having to share a locker room with men (who may think they are girls but when undressed are obviously not) while changing clothes or uniforms.  Do you want your daughters to have to change her clothes in a locker room in view of naked or near naked men.  Of course you don't and if you don't mind that idea, then consider yourself strange.