By brain differences I mean physical differences. Men's brains are bigger and wired differently (more neurons while women have more connections between their neurons). Men think with gray matter while women think with white matter.
All the physical stuff aside, I've never disputed that people can have an identity conflict. I don't dismiss men who say they feel like they are women and vice versa. To me its telling that a woman can feel masculine well before any male chemistry is introduced.
It also seems contradictory to me that some people will say "there is no fixed gender" - yet also claim that someone has "the wrong gender". If nothing is fixed how can anything be wrong? How could a man be stuck in a woman's body if being a man and a woman are artificial constructs? Add that to the fact that a person can have the sense of conflict even before any chemistry is introduced and it seems to me the nature of the problem can't be addressed by chemistry because it wasn't initiated by chemistry.
It also seems to me that if people can deny genetics with regards to sex then why not race? I am a white male but it seems I can claim to be not only a female within but I could say I am a black female. There's no difference really.
With regard to gender I think the real issue for a lot of people traces back to imprinting. Anyone who raises animals knows that if they want to raise a wild animal as a domesticated animal it must be removed from its mother seconds after birth before its imprinted. Its also known that if a baby monkey is taken away from its mum and placed with a family of ducks it will be imprinted with the ducks and try to act like one. Zoologist Konrad Lorenz was famous for having ducks and geese getting imprinted by him and bonding with hims as their mum. Given choice between going back to a real duck mum they stayed with him.
What I am saying is people can have their identity altered in substantial ways. A man who says he feels like he is a woman can have a real conflict. However where he might be inclined to see his actual form as "wrong" or a kind of disease that needs fixing surgically and chemically I would say the acquired identity is more the issue. If the man still the wants hormones and surgery then thats fine with me. Where I see it getting out of hand is in situations like forcing bathrooms to be open to whoever says they belong there. That will lead to abuses and a backlash which is already brewing.
IMPRINTING
http://en.wikipedia.org/wiki/Imprinting_(psychology)