I'm definitely in the same boat as Nigel, and the more I thought about it the more I realized how fucked up it is to "require" that someone go through a surgical (or even hormonal, honestly) transition to be considered legitimate.
I agree but not for the same reason. I hold maleness and femaleness (and therefore manhood and womanhood) to be defined solely by gamete production, something which modern medicine is so-far powerless to alter.
And furthermore, if you acknowledge anything beyond that as a salient or meaningful or relevant or worst of all a defining difference between men and women you're a sexist pig.
I view it this way, e-prime r-prime this is my extremely simplified opinion:
Male =/= man, female =/= woman. Man and Woman are genders, social constructs, and, depending on where you are, loosely embody roles that some people inherently link to those genders. The people who feel like they would be happy in the role of Woman, while being male, are therefore trans, because being Man would suck, and so they want to be called Woman.
You saying that gender and sex are the same thing, and all male are men and all females are women, that point of view is disregarding the wishes of those who want to be Man or Woman despite the sex not matching their gender, and that makes you a dick.