In my opinion, the only common denominator that separates FTCD from TS is whether that person is a man who lives as a woman, or a woman who was born into a male body. This gets complicated because the two can be physiologically and socialogically identical.
What remains is a philosophical question of the difference between a "man who lives as a woman" and a "woman who was born into a male body". I think that the only respectful thing to do is honor what the person identifies as, and forgive if she is wrong. (even she may not know for sure)
EDIT: obviously my example applies to MtF. There are plenty of women who live as men, and men born into female bodies too, so honor their identities as well.
