I know that you're posting AC so you probably won't see my reply, but here goes...
It's amazing that, in a day where we can accept people are born gay, that it isn't a choice, that we will mock and degrade people who feel that their external sex doesn't match their internal gender.
I see one big, important distinction between homosexuality and transsexuality in your example. Homosexuality doesn't require a third-party to participate to make you what you into what your feelings tell you that you should be. Someone who has sexual attraction to those of the same gender is a homosexual whether or not they ever fulfill their attractions. By contrast, it requires active participation to have gender reassignment surgery to "correct" the external body appearance and genitalia.
Let me just correct you right now.
Your argument is that homosexuality is an internal choice. You do not need someone else to recognize you as a homosexual, to be homosexual. It is entirely internal.
Your second argument appears to be that Transgenderism requires an external force -- that transgendered people require a second party to perform a surgery upon them to be transgendered.
This is incorrect. What you are describing is a process some transgendered people go through called "Transitioning." It is not something that is taken lightly (not "deciding one day to chop their dick off" as one particularly vile comment upstream said) -- but rather the result of years of therapy. I don't know the rate of transgendered people who do go through transitioning, but it's certainly not 100%.
Much like a Homosexual person "just knows" they are homosexual, a transgendered person "just knows" they are in the wrong body, that they are the wrong gender. They do not need recognition of this fact from an outside source for it to be true.