What proof is there that being transgender isn't just a mental illness?

Virtually all the science in the last 20 years supports transsexualism being a physical birth condition.

The problem is the general public, as exemplified by your question, don't understand the concept of transsexualism. In an effort to help, I suggest you read the following:

Most people are born with a gender identity in their brain that matches the sex of their body, transsexual people are not. That's what transsexualism is, a birth condition. This leads to a life of pain and misery as their body feels profoundly wrong and nobody ever sees them as the person they truly are. Transsexual people transition (aka "sex change") to affirm their inborn gender identity by changing their body to match and assuming a gender appropriate role in society.

Transsexualism is a scientifically proven birth condition.


A primer on transsexualism:

http://forum.beginninglifeforums.com/index.php/t/15139/f98c4662d36edc533ec0ce09524e746f/


More background information about gender identity and transsexualism:

http://ai.eecs.umich.edu/people/conway/TS/TS.html#anchor107763


A short video of a Stanford University professor discussing transsexual brains:

https://www.youtube.com/watch?v=A3C4ZJ7HyuE
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I was going to answer, but Ms Clones said it perfectly

Well, I am transgender-male to female. And, yes, I have had the shots and the well, body modifications. And I am definitely comfortable with my shape now and my appearance right now. And most guys can't tell-but when I get intimate with a guy, I do not hold back-I tell them. And well, I have learned to defend myself against the idiots that want to kill me.
But I now have a boyfriend that accepts me for what I am-and We are in love. \
So there.......

Look at how society treats them. Do you know of any other 'mental illness' where the patient is so physically and emotionally tortured by others?

MRI scans.

Wrong way around; not being a mental illness is the default state. So you would need to prove that being transgender *was* a mental illness.

Many transgender people do suffer from mental illness, but often this is a consequence of the way other people treat them.

I can't speak for anyone else but when I was much younger, it took me a long time to realise that being told I did something "like a girl" was supposed to be an insult. But everyone thought that, because I had a willy -- and for no other reason -- then I must be a boy. Never mind that I preferred crafts to football, acted out productions of "Joseph and the Amazing Technicolor Dreamcoat" (I had the complete soundtrack on an LP. That's how long ago this was happening. Ask your mother about records -- no, come to think of it, probably better ask your grandmother) with my stuffed toys, wore a small rucksack that absolutely fit the ecological niche of a handbag, oh, no. Poor little me didn't even realise, when they called me a girl, they weren't being nice to me; rather, they just hated women and girls so much that they thought that being compared to a girl would really embarrass me, and they couldn't deal with the concept that I -- supposedly (for no better reason than that thing between my legs) a boy -- might actually prefer the idea of being a girl.

And they probably are the same sort of people who nowadays insist, very loudly and at every opportunity, that I am a man.

Society basically insists that, because I was born with a willy, I have to behave a certain way. Never mind that if you somehow managed to assign a numerical value between -100 and +100 to every gender-related property, and you looked at my figures, then by far most of them (with the obvious exception of "has a willy or a fairy") would correspond fairly well with the scores you would expect of a slightly tomboyish girl. I can't help the way I am. And it's just easier for me to change myself, by formerly changing gender, than to try to change the whole of the rest of Society. And actually, I think if I hadn't begun my transition when I did, I think it would have wound up driving me crazy to carry on living like that .....

In a less sexist society, which didn't hold itself in thrall to the idea that what is between a person's legs is the only impotant thing about them, it's *just* *about* *possible* that people *might* not feel the pressure to go through transition. But note the words "possible" and "might". A society like that is really a totally alien concept to anyone who has grown up in *this* society. We should not expect to be able to reach concrete conclusions from abstract thought experiments, especially not when there are so many variables (basically, how *every* *single* *other* *person* would be affected by a society like that). You might as well say, "if I'd been born in France, then I'd be French".

Pretty much all of actual reality. It just doesn't have to befit your traditional, cultural, or religious ideals as you'd think. I say, even it all, because I just don't want to limit for you all what can be and is relative. I also just don't want to deceive you how difficult your accusation of insanity is to actually prove, either. It is in fact like to enough you'd have to repeatedly explain away, even all fuvcking existence. Just letting you know, before we have to get all into it. No, not even a discussion of the Bible would even remotely be in your favor.