Because SCIENCE, you ignoramus. Treating someone who is simply different from you, or who doesn't conform to your rigidly ignorant ideas about gender and biology, IS problematic for all those folks YOU then ignorantly decide are mentally ill.
Try living in a society in which other people have decided YOU are mentally ill, when you are not, and see if that's not problematic for you.
2. Is being transgender a mental illness?
No. While some
outspoken commentators espouse this notion, there's
no good evidence to back it up. According to the
American Psychological Association, "A psychological state is considered a mental disorder only if it causes significant distress or disability. Many transgender people do not experience their gender as distressing or disabling, which implies that identifying as transgender does not constitute a mental disorder." Moreover, the World Health Organization
no longer classifies being transgender as a mental illness.
While transgender identity is not a mental illness, transgender people and those experiencing gender dysphoria are more susceptible to depression, anxiety, and
ADHD. However, a
systematic review found that psychiatric symptoms vastly improve following gender-confirming medical interventions. It seems that when transgender people are permitted to assume their gender identities, they become happier and healthier individuals.
3. Are there brain differences associated with being transgender?
Yes. Male and female brains are
structually different, and fascinatingly,
studies show that the brain structure and brain activity of transgender people more closely resemble those of their gender identity versus their birth gender.
This suggests that sexual differentiation of the brain during the development is not necessarily linked to sexual differentiation of the genitals.