Interesting, I didn't think any part of what I wrote would be seen as controversial.
> Someone can self-identify as a gender (among other things),
I do this everyday. It happens to match my biological sex, but it doesn't have to. This is probably what makes some people uncomfortable, but a biologically determined gender binary is hardly a universal human truth.
> alter their appearance to present as such,
We all alter our appearances to present in a way we find most useful, pleasing, or comforting. This doesn't seem controversial.
> and a kind and empathetic society will (should) then regard them as such.
I would hope that this part isn't controversial and would be something we all aspire to.
In contrast, I believe that the contexts you've provided (prisons, sports, locker rooms) have been demonstrated to be largely politically motivated controversies with very little real-world evidence for the claimed harms.
A similar situation exists for the medical claims. I believe you're alluding to medical interventions for gender reassignment for young trans people. There have been studies[1] showing that the interventions significantly lower suicidal ideation:
> "Among transgender adults in the United States who have wanted pubertal suppression, access to this treatment is associated with lower odds of lifetime suicidal ideation." [1]
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7073269/