While homosexuals, bisexuals, and transsexuals have unique concerns, we all share deviant sexual desires and behaviors. That doesn't mean that the etiology of our deviances are the same, or that we are all variations on a common theme.
What we know about transsexuals is this: They state a desire to be and appear to be, the gender opposite of the one they have. Plastic surgery and hormone therapy can reshape the body so that it superficially appears to match the desired gender. This seems to relieve the discomfort of discordance between how they appear and how they wish to appear.
As far as I know, (and as far as I have observed in ordinary contexts) there are no biological markers for transsexuality. There are no physical features that identify transsexuals. As far as I know, the critical test for transsexuality is a
fervently defended consistent narrative. However, most transsexuals seem to enjoy the changes brought about by hormone therapy (feminization or masculinization) as well as the changes that can be brought about surgically (breast/ovaries/penis/testicle removal or vagina and penis construction).
It is one thing if reasonably mature gay men decide that they really would rather be women, or a heterosexuals decide they would rather be the opposite sex. We can be doubtful and wonder if there isn't something slightly crazy about the whole thing, but at least they are adults.
I for one am not willing to accept that 4 or 5 year olds declaring that they want to be the opposite sex should be given the benefit of the doubt. To put it bluntly, I am suspicious of the parents, cooperating school authorities, and medical officials who aid or allow children to act out any sort of transsexual fantasy. It would not be the first time that incredibly naive (or stupid) theory was applied to young children. It also wouldn't be the first time that parents imposed inappropriate ideas on their children.
The thing about homosexuals, heterosexuals, and bisexuals is that they can demonstrate the validity of their preference by performing what it is that they prefer. Consistent arousal in a same sex or opposite sex situation provides physical proof (if anybody needed it). Further, there is the consistency of fantasy and arousal.
I suppose it can be said that transsexuals also demonstrate by performance the validity of their condition. What is more difficult is for a transsexual to demonstrate arousal. If they have been given hormone and surgical treatment, the body parts that show arousal may not be there any more, or may not work as they did before hormone therapy.
I am not in favor of categorizing adult transsexuals as
people who only engage in very elaborate drag. The people who have embarked on transsexual transition have often had to endure too much brutal public ridicule (and a good deal worse sometimes) for it to be considered merely an affectation. This is especially true for transsexuals operating on a shoestring. Clearly they are committed.
On the other hand, people are prone to believing their own bullshit. A lot of empathetic types who want to be sensitive on the issue accept pretty much everything transsexual advocates say without too much critical questioning. More critical thinking is needed here, and not just for pro-advocacy.