It makes perfect sense if you can remove genitals from the equation. The mind is the key to how one identifies. If I identify as female and am attracted to men, that is considered "straight", and since my physiology doesn't line up with my mind, I am transgendered/transsexual. That is how one identifies as a straight transsexual. How one identifies has absolutely nothing to do with the genitals, it just happens to be that with most people, the mind and body line up.