This is based on a comment from Chairm, in my discussion with Jose at Opine:
Gender is a lot more than a social assumption. This is the same mistake many feminists make in their effort to break free of the restrictive gender roles of our patriarchal culture – they mistake gender roles for gender (or vice versa). Gender is our subjective, "sexual Self-Map, how we feel ourselves to be: male or female." (Bushong) "Like pain, it is unambiguously felt but one is unable to prove or display it to others. One's subjective gender is just as real and immalleable as one's physical gender but unfortunately not recognized in our culture."
So while it is true that I am not a genetic woman, and cannot share the complete experience of what that means (as far as the physical, embodied experience of living in a female body, and also as far as socialization from birth), it is at least as true to say I am a woman as it is to say I am a man. Probably more so, because gender identity certainly appears to be more immalleable than physical bodies.
In the same way, can you say whether an intersexed person is a man or a woman? Their bodies are ambiguous; so my gender is ambiguous. I'm neither man nor woman, but transwoman – some of both. I choose to live as a woman because it's a lot more comfortable. And that's not a bad thing, even though our culture works hard to make it so. It just is. It's beautiful in its own right. Between day and night is the beauty of twilight.
Gender is not plastic, but gender roles are. Gender roles are defined and delineated by culture and society, and they change over time and from place to place, culture to culture. When I speak of living in the role of a woman, I'm speaking of sharing that gender role with other women in our culture.
Given our culture and the discrepancy between sex and gender (or physical gender and gender identity), one of the biggest challenges faced by transpeople is integrating mind and body. Certainly that's been one of the hardest things I've tried to do, but, thankfully, I have had some success with it. I've still got plenty of room to grow there, but it is, I think, an important – maybe the most important – aspect of the peace that fills my life. I believe that there is a Universal Being (usually called God) which creates us all – Life, Love, Mind. Which means that I have a purpose in being a female person in a male body. That purpose is to love, but it must also be more – perhaps to demonstrate the integration of male and female aspects in the fullness of humanity, I don't know. Or maybe it's just a cozmic joke. :-)