I think I agree with you (I'm sorry but it is a very long post, and a bit of a wall of text at times!). If we accept that gender (as opposed to biologically-defined sex) is a socially constructed concept, then we are also committed to saying that it would not exist outside of society.

Given that, we can also say that, abstracted from society, individuals are neither man nor woman, trans nor 'genderfluid'. Identifying as being a particular gender will then really be identifying as a particular gender in a social capacity. The feeling of being in the wrong body then, as a trans individual might, is the feeling of being socially regarded as a gender they do not recognise their self as being. I do not know whether the latter is true, but certainly, I have never given much thought to my own gender identity, I have simply gone along with it out of custom (using the specified toilet, ticking the appropriate box on a form).

Gender, in my view, is such a contentious issue in the current climate because it still holds so many cultural associations which individuals wish to reject. When those associations inhibit their will, they are understandably annoyed. Those associations will likely never disappear, but I suspect that, in time, their significance will diminish, as society comes to terms with the individualism which continues define it; which is to say, in a world where we cannot presume anything about anybody based on their race, gender, sexuality or whatever else, we will, inevitably, have to treat each as a clean slate.

While this is a good thing, the interesting question is how we will determine the manner in which we value the different aspects of a person. Just because we are moving away from the judgement of persons based on unavoidable characteristics, does not mean we will not be making value-laden judgements about persons.