Diversity of gender identity, in our society that is currently structured around a gender binary, is an essential right. Without it, transsexuals and transgenderists have limited statutory basis for assignment to gender-appropriate housing, whether in a college dorm or a prison cell. But while diversity of gender identity is an important component of a diversity-affirming society, it does not affirm the right of those with more static identity to crossdress or otherwise play with or periodically change their gender. It would require them to revise their internal and external notions of identity in order to do so, hardly a liberating concept. Protecting freedom of gender expression would protect such behaviors.
Gender expression is a function of behavior, voluntary and involuntary.
It includes facial appearance, vocal intonation, as well as general body carriage and movement. These may or may not be associated with the formation of an identity, and may or may not be protected by statutes protecting diversity of identity. There are many men who crossdress and for whom discovery of that pastime could lead to disastrous consequences arising from erroneous presumptions about their morality, mental stability, or simple trans- or homophobia. Although a recent Supreme Court ruling arguing for a wider interpretation of human rights protective legislation coverage promises to improve the outcomes of court challenges to discrimination, we cannot presume that existing law will be interpreted to protect the rights of those who crossdress recreationally. And social movement towards acceptance of crossdressing without such laws has been glacial at best.