@GarlicMist - I made a statement about my experience and the experience of trans people I know and you generalise that into a massive straw man.
I grew up with female best friends. My peers were primarily girls and I went through all of those experiences alongside them whilst doing a lot of the same questionnaires looking at my own gender and trying to figure out where I was. I've been there and seen some of the very darkest sides of this in my friends (trans or otherwise). Please don't think I'm ignorant to female or feminist issues - quite the opposite.
On a more general note the majority of trans people don't have repressed homophobia. It's very easy to offer an external diagnosis about trans people based on their sexual attraction (and well done for totally erasing bisexuality like the week after bisexual pride by the way). An awful lot of people I know identify as bi or pansexual, some with preferences one way or the other.
Now I believe that biological sex and gender are different things (as is gender expression). But of course some people don't understand that. Trans activists (and I count myself as one) explain this all the time and the model makes sense. For most people all three are in line. For some people their gender expression can vary from their own gender through to androgyny and out the other side. I think everyone agrees that this is a good thing and freedom of personal expression is important and isn't something you should be attacked for.
But the middle one - your internal feeling around gender - is a mix of your life experience, societal impact, brain chemistry and hormone balance. There is science behind this (my natural oestrogen level was almost double the top end of the range for a male for instance - and I had bilateral Gynecomastia).
There is still research required into this and I'm a firm believer in science. The whole pink vs blue brain concept is flawed - it's going to be shades of grey like everything in life and different parts of the brain are going to be wired differently (for instance in my case I have very high emotional intelligence, compassion and empathy - I get a lot of satisfaction from running support groups and helping other people which are traditional 'feminine' traits). But you also need to factor nurture into this.
The thought experiment of a genderless society is interesting. I suspect in a large enough peer group you will get some that identify with their peers of different genders. There is evidence of trans people through history so it's hardly a modern thing. Different cultures had different approaches to gender historically and it's a fascinating area of study.
It's very easy to say we are animals and have dimorphoic sexuality but you also need to realise that we have intelligence, intellect and individuality far above any other species we know.
No other species has done anything like what humans have done - so using biology as a simple comparison seems flawed as it erases the one thing that separates us from the other animals - our minds.
@WankingMonkey - that anecdote is the future for me as well. Seeing people able to have whatever gender expression they want and also dismantling misogyny as well. Boys can wear makeup (and frankly some look amazing). I know quite a few trans girls that are makeup artists and their skills are outstanding.
Getting the rest of society the accept this is one of the challenges we face. Just being accepting to someone who is dressed a little differently is a massive challenge. And ironically it is almost always men that make the transphobic comments, usually to reinforce their own masculinity and cover their own internalised homophobia or doubts. And then probably go home and watch trans porn!
As to online trans support groups I am a member of quite a few closed FB groups and various other online spaces and most of what we discuss is nothing like those links. Primarily it is emotional support (suicide and self harm is quite prevalent), discussing hormone treatments and In the U.K. offering advice around the NHS system or bitching about how slow it is.
There is almost zero sexual context in any of the groups I'm involved on. In fact anything sexual tends to get you kicked (the last thing we want is chasers/admirers in our spaces - that we can agree on).
That is the difference between trans people and the AGP/ fetishistic side. A lot of cross dresser forums are incredibly sexual and I try very hard to differentiate myself and other trans people from that.
I'm not saying trans people are asexual - far from it. But our desire for sex and our desire to be accepted in our preferred gender are totally separate things, not mixed up together.