I always explain it to the point that, its not about what we are, its more about what we wish..
we arn't simular,
we are diffrent gender, sex, have diffrent sexual orientation life, lifestyle, and so on.
but we have few things in common about how we want to be accepted and respected.
I think the part who bind the GLBT is actually "gender" and "sex" and freedom to love people regardless of those. (which also include transgender)
without that part, we can't even discuss the sexualety part of gay, bi, or anything ells..
as it said before I dont belive it to help us standing alone, I belive as a bigger group we stay stronger, but I also belive as a bigger group it demands more accept and tolorance from all of us.
people wont take us seriously for accepting our diffrences, if we cant accept our own diffrence parts in the group.
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beside those, its fact that no matter what sexualety we have, we are in some way on the same situations as people with diffrent sexualety in one or another part.
ex: a gay ftm, will face the same discrimination as any other gay guy,
but a straight ftm, can also face discrimination, ex if the person isnt legal male, they might not be able to get marrige.