Honestly,

I've done as thorough a dig through the scientific literature as I am able to (through pubmed).

Here's what I've managed to come up with, in case you are interested in what the research says:

1. Baseline Physiologic and Psychosocial Characteristics of Transgender Youth Seeking Care for Gender Dysphoria;
2. White matter microstructure in transsexuals and controls investigated by diffusion tensor imaging.
3. Structural Connectivity Networks of Transgender People.
4. Increased Cortical Thickness in Male-to-Female Transsexualism.
5. Gender dysphoria "cured" by status epilepticus. (this one is just interesting)
6. Sex dimorphism of the brain in male-to-female transsexuals.
7. The biology of human psychosexual differentiation.
8. Transsexualism and sex-related differences in hemispheric asymmetry.

I would characterize these studies as being incredibly preliminary, and most are from within the last 5 years.

They all have incredibly small sample sizes, and their results are contradictory, often finding no physiological difference. If there is a physiological indicator shown, it is something that can only just be considered statistically significant. No attempt to replicate any of the studies here has been done, to my knowledge.

So given the paucity of scientific data showing that transgender or gender dysphoria is a physiological or medical condition, compared to a psychological condition, how is the current standard of treatment justified, given that it typically involves powerful hormone treatment (with incredibly damaging potential side effects), and surgery that would be considered obscene mutilation if it were done for any other reason?

Frankly, I expect that 20 years from now we will be looking back on this era in the same light that we look at lobotomies now.