Laura Pappano and Eileen McDonagh argued in their book, Playing with the Boys: Why Separate is Not Equal in Sports, that the continued separation of the genders (for the purpose of this post we'll go with the rather simplistic construction of gender as a binary system) harms women's athletic participation. Note that their argument is more nuanced than that one-line synopsis as they compare the historical and ongoing separation of boys and girls and men and women in athletic endeavors to the cultural and political separation of races in the United States and discuss the damage done by failures to integrate, by gender, sports.
This is an ingoing debate in the study sport, gender, and culture and I myself haven't come down on any particular side (shocking, I know!). What worries many, myself included, is that we just don't know what will happen if sports that have not been integrated (and some certainly have and some certainly should be--hello, billiards??) begin to move in that direction. Will women lose opportunities that have been gained over the past three plus decades (in the U.S.)? Will girls be dissuaded from or discouraged by playing with boys? And note that that is the way this is being framed (not necessarily by Pappano and McDonagh but in the general discourse): girls joining boys on their teams.
It looks like we are going to start seeing some data--from Canada. High schools in Ontario have recently decided to let girls play on boys' teams. And people are abuzz about it with some arguing that elite level athletes, like speed skaters and hockey players, have been competing against men (largely in practice granted) in order to improve their skills. But others suggest that the move will deplete women's teams and leagues of their best players and may ultimately lead to the elimination of women's team and leagues altogether--which would, in turn, lead to more women and girls dropping out of sport altogether.
In other words, the debate up north is very similar to the one we have been here. But I am very interested to see how this plays* out.
*Yes, the pun was intended!