On this idea that believing someone is a man 'takes away' their idea they are a woman. I remember during the gay marriage debate, Evangelical Christians got very upset with the idea of gay marriage because they felt it tarnished their own marriages and ruined the concept of marriage for them. As people correctly pointed out, this made no sense. Someone else getting married in a way you disapprove of has absolutely no impact on your own relationship. What other people do in their private lives cannot possibly affect YOUR life.
It's interesting to see some trans people making similar arguments to the Christians. If I don't believe that someone is really a man or a woman, that belief doesn't impact on them in the slightest. They are still entitled to believe what they like about themselves, and (to paraphrase John Stewart Mill here) there is nothing I can actually do to take that belief away from them! Unless they are saying that their sense of self, or beliefs, are so weak that they need absolute agreement from everyone else to prop them up...but it's accepted that no one has a right to everyone believing the same things they do in order to shore up their identity.
I've been called a man before, I've had people doubt my bisexuality, I've had Christian friends who don't really believe I'm atheist (I must SURELY hear god speaking to me at least sometimes.) None of this bothers me at all. Them disagreeing with me has no impact whatsoever on my identity. It doesn't make me less of a woman, or bisexual, or atheist - it can't possibly take anything away from me because it's just not the kind of thing you can take. So while I feel sorry that Katy feels their womanhood is being taken away by the beliefs of others, my sympathy has limits because the simple answer is that people will disagree with you and you just have to live with it.I'm amazed that people can get through to adulthood under the delusion that everyone has to agree with them or else their identity is threatened.