Just writing in quickly to say.
I don't know why some (many) posters go on about gender identity being a feeling in such a confused and astonished way. As if I must be an absolute idiot to not understand why that's what, silly? To base someone's reality on a feeling?
But again this is a natural part of being a human being and society is literally based on the feeling of the citizens within it. We do not make laws (or many of them) because they are identifying hard facts. We make them based on the fact that the current mood or culture believes, for example in the case of criminal law, on moral values, an entirely feelings based concept. Homosexuality was illegal. Now it isn't. There are no tangible factual reasons for it to be legal or illegal, the only difference is if society at large feels it to be the case.
So when I'm accused of skipping over defining gender identity as anything more than just a feeling, it's because the argument is being overcomplicated. It is a feeling. But it's a consistent, life altering sense of self that a reasonably significant amount of people hold. It being based in feeling does not make it any less valid. If anyone here struggles with the word valid I would point them to a dictionary.
In this context, it to me sticks fairly clearly to the normal definition of the word. If someone's concerns are valid, it means they have a basis for their concerns in logic or fact. I imagine it is used in the context of trans people more because people with view points such as those seen here, with those saying that transgender people can't really or shouldn't really even exist are literally invalidating their existence as a trans person - as in saying their sense of self is invalid due to it not being valid, as it is not based in what they see as logic or fact.
Just to tonally clarify, again this is not an emotive statement. I'm just explaining and think you would agree that if you assert the position that gender identity doesn't exist in any meaningful way, then therefore you are saying anyone prescribing the idea of a gender identity different to one's biological sex is making an invalid claim to you. Which I'm sure you can agree is an accurate way to describe what is being said here on MN.