Just like you can't change your species, or your age, or your race. You either have the XX chromosome or the XY. Mutilating your body to imitate the other sex doesn't change that.
Sexual identity problems should be treated the same way any other mental issue is treated. One article that I read drew a very good parallel with body integrity identity disorder, where people feel "wrong" unless and until a part of their body is removed or they achieve some other handicapped status (blind, deaf, etc.).
ἡ δὲ κἀκ τριῶν τρυπημάτων ἐργαζομένη ἐνεκάλει τῇ φύσει, δυσφορουμένη, ὅτι δὴ μὴ καὶ τοὺς τιτθοὺς αὐτῇ εὐρύτερον ἢ νῦν εἰσι τρυπώη, ὅπως καὶ ἄλλην ἐνταῦθα μίξιν ἐπιτεχνᾶσθαι δυνατὴ εἴη. – Procopius
Ummaka qinnassa nīk!
*MySmiley*