Inferior treatment begins when you make assumptions (i.e. transgender folks are all mentally ill). It's called "implicit bias," and it is heavily researched in psychology. Yes, it has an effect even when you aren't aware of it.
I'd really like to know the "many other health professionals" who believe that transgender identity is a mental illness, because if this is correct, I'm very concerned about the medical field. As a psychologist trained in diagnoses, I know mental health diagnoses probably a little better than you, and Gender Identity Disorder is not in the DSM-V (2013 is when it came out, so you seem to be behind the loop in diagnoses); it was, however, in the DSM-IV TR, and then was removed because it unfairly stigmatized all individuals who didn't fit into a gender binary as mentally ill. "Gender dysphoria," on the other hand, is a CURRENT diagnosis in the DSM-V that sometimes fits for those who are transgender but experiencing extreme dysphoria as a result of the incongruence between their internal identity and their body/external experience. Not every individual identifying as transgender fits that diagnosis, so no, not all transgender individuals have a diagnosable mental illness. It's interesting and a bit condescending to assert that you know more about mental health than someone trained in mental health diagnoses, well-read in bias/prejudice research, trained in gender identity concerns, and trained to treat folks with gender issues. But it seems that you'd like to explain my knowledge base to me as if you know it better...
