Dr Reed, you make very eloquent points, however your heteronormative decision to use male pronouns with which to refer to Caitlyn Jenner distracts from that immensely. Hearing feminist discourse referring to women as 'dames' would be similarly jarring. I am always amazed by the need for people to refer to others with names or pronouns that cause the referent pain. If someone prefers to be called by their middle name do you insist on using their first?
As a physician who has treated hundreds of transgender patients for over a decade, and as a transgender person myself, I would like to answer some of the questions you pose.
"What does any transgender person do before the moment of coming out?" In a word: suffer. There is a truism in psychology that people only change when the pain of changing is less than the pain of staying the same. With the amount of stigma, transphobia, and discrimination they face you can imagine how significant that pain must be for people to transition. I have treated countless people who showed up at my clinic at the point where the decision is transition or suicide. This is why non/pre-treatment suicide rates are in the 20-40% range. Moreover the stigma is quite unbalanced with transgender women (like Ms. Jenner) facing the lions share compared with transgender men like myself. While transgender people are a smaller population than LGB people, in 55% of all hate motivated murders in the US, transgender women were the victims. Moreover the lions share of that mortality is faced by transgender women of color. Even though she is white, Ms. Jenner is an aberration not only in her political leanings but in her socioeconomic status as well. Poverty, prison, rape and homelessness are facts of life for many transgender women in America. That reality is multiplied many fold for transgender women of color and those who live in poverty. (I would link to a reference available from the National Coalition of Anti-Violence Programs - but as a new registrant, I can't.)
"transgendered people’s are true immediately provokes a "Who says?" Modern evidence based medicine? Specifically the AMA, both APAs, ACOG, the AAP, etc. You make assumptions that the arguments for transgender identities are somehow just based in discourse about identity politics. For example, just as twin studies speak to the heritability of sexual orientation, they also speak to the heritability of gender identity - between 30-60% of the expression of cross gender identity is likely heritable. Do you make the same 'who says?' argument about sexual orientation?
"I’m pretty sure that in most of the United States it’s still marked on one’s birth certificate. That’s not the delivery room, but it’s pretty damn close." And doctors famously got that wrong in many instances of people with intersex conditions. They also get it wrong in the case of transgender people. If they did it with race or sexual orientation they would get it just as wrong too. You are assuming a level of competence or certainty that simply doesn't exist in medicine. Moreover I have a friend and colleague who delivers babies and she tells the parents: "well your child was born with a penis, and most likely that means he's a boy. But we won't know for certain until your baby is old enough to tell us". She certainly has patients who have selected themselves based on her practice otherwise, but she's never had a negative reaction from that.
"gender is a 'fundamental attribute' of our existence. But gender is no less culturally constructed than race." Why do you insist that these two ideas are mutually exclusive. I've asked many transgender people the following question: "if you were going to be on a desert island for the rest of your life and never see another person, would you want hormones and surgery before you went?" The answer is universally yes. Gender is a fundamental internal sense of ourselves as male or female (or somewhere between the two). The wrongness felt by transgender people is not just due to the way others treat them, but also based on the body in which they live. However gender is also a cultural construct that places immense social pressure on people to conform to idiotic concepts of maleness and femaleness. Transgender people's internal gender dysphoria is compounded by navigating these cultural constructs but it is not simply the result of them. In fact, that idea - wanting to transition simply because of the social benefits of the other gender is a rule out in the diagnosis of Gender Dysphoria in the DSM-V.
"how can we legitimize transgender identity... without the psychological stigma of dysmorphia" You can't. However there is a tremendous amount of gender dysphoria that transgender people suffer before transition. I've personally experienced it and I have seen it in every patient I have treated with the exception of those who are post transition in whom the dysphoria abates to a non-clinical level. It does get better but like treating cancer or diabetes, active treatment is necessary. Moreover the pathology is not in the identity but in the dysphoria between one's identity and body. Make the body congruent (enough) with the identity and the problem is mostly solved.
I will admit that there are many in the transgender community that are vehemently against 'pathologization', however they are both wrong from a scientific and nosological perspective, but also misunderstand what would happen were the diagnosis of gender dysphoria made to disappear. The only argument to allow people in prison or people dependent on government sponsored insurance to be able to access care is that of medical necessity. Without a diagnosis such necessity cannot be supported. However in my experience those who are most vehemently opposed to such a diagnosis are generally educated white transgender women from enfranchised backgrounds. One case regarding a prisoner on which I consulted a number of years ago required me to make the argument for medical necessity and I asked the attorney to ensure her client was OK with that. The response was that she wouldn't care if I called her a mass murderer who practiced bestiality on chickens (stated more colorfully than that) - as long as we could get her the services she needed. Unfortunately those who most need the benefit of the diagnosis often never have a place at the table when discussions of depathologization occur.