It's simple: boys in the Boy Scouts, girls in the Girl Scouts.

Its very simple.  It's all in the very title of the two organizations.  Boy Scouts.  Girl Scouts.  One's gender is essential for membership.

But wait!!  The glbt community has something to say!  Something along the lines that a penis does not make a person male, and a vagina does not make a person female.  Okay then... it's time for me to go when people believe that sex and gender aren't the same. 

When they slandered me as a "homophobe," I came up with "heteroseparatist."  When they slandered me as a "sexist," I came up with "genderealist."  Why do some people reject the fact that over 99.9% of human beings are completely XY or XX?!?

What has this world come to when, "I want to be a boy," is accepted as truth when the person making the statement was born female?

More detailed information here and here.