There are a number of people who identify as genderqueer, as having gender identification that shifts over time, as crossdressers, as drag kings and queens, as on some point on a spectrum, as a third sex, or in a number of other ways that are not as simple as "I was assigned the gender [male/female] at birth, but I am really [female/male], so I have transitioned/am transitioning/will be transitioning." Supposing that either people are cisgender (were assigned their correct gender at birth) or transgender (assigned the opposite sex at birth) IS reductionist. Transsexuals, however, are people of which that case is true, and the fact that this is not true of others doesn't change that.