Transsexualism is an autoerotic fetish. Masturbation is autoerotic, and too much of it can lead to erotic target location error, causing autogynephilia in straight men. This causes men to fantasize as the opposite sex during masturbation. This, combined with narcissism and other comorbidities, including possible imprinting, leads to the transformation fantasy where a man wishes to castrate himself and take hormones to impersonate the opposite sex. In western nations, it is now largely autogynephiles who transition, there are only a few dozen children who are being transitioned in the whole US. There is a minority of MtF transsexuals who are homosexual and spontaneously flamboyant, they used to be a larger percentage of transsexuals, but now being gay is socially advantageous, so it is only somewhat common in like southeast Asia and Brazil and stuff, this type of trans.
Otherwise many MtF are lesbians.
FtM trannies are just angry women with penis envy. They like beards or whatever. Autoandrophilia sort of, which is also what makes gay men want to work out and grow big beards. But women don't really have much of a fetish drive, though they can, and with testosterone, can get really fetishistic.
