A lot of different angles--e.g., no one questions correcting vision (glasses, implants, surgery) to compete so... why not correct a testosterone deficiency with a little supplementation?
It would make as much sense as being told to take drugs to erase a competitive advantage resulting from a 1-in-a-million genetic aberration-- especially so if the anomaly is essentially nothing more than how you've come to think of yourself when it comes to your gender-assignment.
But then... isn't that the slippery slope... e.g., not seeing it as a big (illegal) leap to think you ought be able to even up things when all your competitors are doping?