The whole concept of autogynophilia rests on the assumption that doing something because you find it sexy is wrong. Which, fuck that. If there are guys out there who genuinely derive sexual pleasure from the idea of being women and yet somehow they aren't actually trans, excelsior to them I say. I support them in their quest for sexual satisfaction.
I mean, that's horseshit obviously, but if it weren't, it still wouldn't be a good reason to deprive trans people of their rights.
You should be allowed to transition just because it gets you off. There, I said it.