Thanks to all who commented on my original post. You provided me perspective and encouragement. I was especially reassured simply by how fast you all responded! I am grateful for this supportive community.
I've been following up on the matter, so I thought I would share my latest writing. For context, I have complained to the supervisor (without using the word trans, oops), stopped going to IOP, discussed the entire issue with my therapist, and written this email. Let me know what you think!
Hi [supervisor], thank you for taking the time to speak with me earlier this week, and for your help as I sorted out my treatment options going forward. Now that I have had some space to process, I realize I didn't make it fully clear what was said and why I found it objectionable.
In a discussion about healthy at any size, an idea I largely agree with, [dietitian] mentioned how this is an important activism topic for her, and shared that she had recently read a post by another activist that said that it is transphobic to assume that people who take cross-sex hormones are unhealthy. I have many problems with this statement, as well as its timing.
First, this statement is medically inaccurate. It might not be kind to make assumptions about other people's health, but it is true that increased levels of testosterone in females, and estrogen in males, do lead to health issues. There is decades of research, data and anecdote, demonstrating that high testosterone in women can cause PCOS, uterine and vaginal atrophy, painful periods and orgasms, hirsutism, acne, and more. Long-term use of exogenous testosterone also leads to infertility, by way of medically recommended hysterectomy, which has its own list of health implications. The list of side effects from long-term estrogen use in males is just as long.
Second, this statement was triggering. I have been accused of transphobia, as well as cursed at and called names, for arguing that defending women and their rights is not inherently an attack on people who identify as trans. I simply believe that it is not possible for humans to change sex, and that distinctions between men and women, males and females, are necessary for achieving liberation for women and girls and equality between the sexes.
This was not the first time that [dietitian] has made comments that suggest that she does not hold these beliefs. ("Menstruating people" is female-erasure, and "men and women and people who identify as non-binary" undermines sexual dimorphism.) Because of this, my history of abuse, and the abuse directed at me and women like me who oppose this language (J. K. Rowling and the trans activists: a story in screenshots) I did not feel comfortable speaking up in the moment and have struggled to articulate what set me off.
Finally, it was inappropriate for such a statement to be made in the middle of an eating disorder nutrition therapy group centered around overcoming diet culture and promoting body acceptance. On the surface, it is inappropriate because it takes what is supposed to be a therapeutic conversation into a political subject fraught with controversy. Further, it is inappropriate to imply that I am hateful or afraid because I have different beliefs about this issue.
More deeply, and most concerningly, the comment promotes an ideology that normalizes body dysmorphia. "Trans" is the idea that there exists a certain set of people who are "born in the wrong body" and that these people must undergo dangerous medical procedures in order to make their bodies resemble to opposite sex. That is, it is the idea that there is something wrong with your body, that obsessing about your feelings of discomfort in your body is valid, and that you should do what you can to alter your appearance. This is not, as [dietitian] presented it, a healing, body-neutral narrative; this is body dysmorphia.
I hope that this has clarified my position. It is my hope that [treatment center] and [dietitian] will understand why it is concerning to me that this is a permissible subject in your facility. I didn't even get into how this relates to my autism--that is a discussion for another time, but please let me know if you have any questions.