Interesting, however I have to ask.
What of the individual and his concern for the body? For me at least I think that my feelings concerning these issues stem from the incongruity between my self (that is the "me" my conscious being, of which I believe gender is part) and the body I possess. I feel these issues would arise irregardless of a society that fully accepted them and allowed me to lead the social role I desire. Even if I were permitted to act and feel the way I wanted to, there would still be this bodily distinction whether the society embraced it as it does now, or did not.
Of course I would never be so obnoxious as to claim certainty! Especially on such issues as these. I am sure some would be happy in your theoretical ultra accepting society. However I do not think they all would. Also this differentiation can still be pinned upon the individual and his feelings as opposed to the society. I
think you could only blame society as the prime cause of "trans angst" if in your thought experiment it caused all trans people to be happy with their situations.
Then again maybe there is no prime cause after all!

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Please note:If I appear blunt or rude in
discussions I apolagise. Three years of writing philosophy papers has given me quite the confrontational writing style when it comes to these things, and I have been misinterpreted in the past as being an arrogant ass. Well I think it was misinterpreted anyway!