Transgender is NOT a mental illness. Transgender is NOT "playing pretend." Transgender is a legitimate, scientifically observable neuro-physiological condition which occurs during fetal development, and the people who suffer from this condition should be acknowledged and covered by health insurance providers.
All human (and other mammalian) embryos are inherently female at the time of conception. To develop into males, the embryo is exposed to a series of chemicals which alters their DNA and physically "rewires" the neuronal structure of the brain to that of a male. The problem is, there are two different groups of chemicals: one causes the body/DNA to become male and the second causes the physical neuronal structure of the brain to become male. If a developing fetus is exposed to either set of chemicals without the other, the baby will be transgender.
This has been scientifically demonstrated, and the difference in neuronal structure between the male and female brains can be proven and observed using Functional Magnetic Resonance Imaging (fMRI) of the brain. Since males and females had different evolutionary purposes before the advent of modern society, different areas of their brains are more or less active - for example, men tend to process information visually and think in practical terms, while women tend to process information through reading/writing and think in abstract terms - and these varying levels of activity between lobes of the male and female brain can be readily observed by fMRI.
An accepted biological explanation of the condition, and a valid medical test which can confirm its presence in an afflicted individual. Health insurance providers should require nothing else to provide these suffering human beings with the surgical procedure that they need to live healthy, fulfilling lives.