The attitude that "that person was x so s/he will never be y" and the discomfort knowing about the changes causes in a lot of people are typically why out (and outed) transpeople get discriminated against, harassed, beaten, and too frequently killed. (See
Remembering our Dead)
There is more to all of us than we show the world. How are transpeople that different, other than the profound transformation of their bodies to reflect their internal state? We have rejected the "biology is destiny" role as women. Why not afford the same to those rare individuals (about 1 in 10,000) who feel a fundamental mismatch between their gender and their bodies?
Note to self: actually purchase
Evolution's Rainbow: Diversity, Gender, and Sexuality in Nature and People