slightly off-topic:
As you suggest, gender identity is psycho-social, the body functioning as the main site through which gender is expressed. To the extent that one identifies as trans, he or she is uncomfortable with the lack of congruence between their ascribed gender and how they fell in terms of immediate identity and desire. While physiological techniques can facilitate transition toward outward expression of this gender-identity, they are just the tip of the iceberg, as those who can successfully pass in drag demonstrate. So why manipulate the body at all? Well, hormonal therapy, top surgery, and bottom surgery all mold the body into something that appears and functions more congruently with their internal identity. Put simply, it's easier to perform socially as a woman when one can more easily 'pass' as being female. Also, many patients report the mental effects of hormonal therapy leading them to feel more comfortable in their own skin, for whatever reason.
If the surgery could give those who have it sexually functional alternative equipment it would be different
Er, the results of 'bottom-surgery' are indeed functional, and most patients retain the ability to orgasm. If we're talking about "function" in terms of procreation, well, this is just a small part of sex for a lot of people.
the superficial changes are rarely effective enough to cause others to perceive those who undergo them as the opposite gender
How have you determined that? It's the nature of passing as another gender that people will not be able to visibly identify the individual as transgendered. I actually have a couple of trans friends who rather easily pass as their chosen gender. The rate of identification as trans is roughly .3% of the population, so if trans people were widely unsuccessful in their social performances, you'd be spotting a far higher number of 'unsuccessful' transgendered performances walking down the street.
It's extremely unfortunate that so many people are so unhappy with the sexuality they're born with that they're willing to take such drastic measures to look a little different, but in my judgment "unfortunate" is all there is to it since gender reassignment technology simply hasn't advanced far enough to do anything practical about it. If I'm missing something big here I don't know what it is.
It should also be noted that not all individuals who identify as trans undergo hormonal therapy, top surgery, or bottom surgery. And not all identify as the opposite gender; some reject the gender binary entirely, identifying as "both", "neither", "gender queer", etc. I think what is unfortunate is that our culture has adopted such a strict system of binary gender that it is hard to negotiate life as transgendered without firm identification as the opposite of one's biological sex. Our current system of gender is not culturally ubiquitous, so it seems that it may later evolve (or be actively transformed) to allow for a wider spectrum of gendered performances. Under such circumstances, identification as transgendered would be another animal entirely.
And this is not getting into the non-trivial incidence of intersex individuals (the rate is roughly 1/2000).
ebola