But isn't the maintaining of such labels a perpetuation of the social stereotypes of men and women?
Definitions such as homosexual, bisexual, etc make sense because they are referring to sexual orientation. The "expressive sex" of man and woman, rather, would not exist if we didn't stereotype men and women based on their actions.
Look at examples such as tomboys. They perform in most ways like a heterosexual female: they have female organs and are attracted to males. Yet they act in some manners in ways that usually are considered the domain of men. Where does the line between tomboy and transsexual even lie?