Woah, I'm not going to quote you Drew because that's a little more than disturbing. We're talking about this happening at the embryonic stage, not some little boy saying "mommy I want to be a girl." In response to Carl, it's not quite like that, because the embryo/fetus isn't actually altered in any way. In other words, if your parents had undergone this selection when they concieved you, and wanted you to be a girl rather than a boy, there is a 0% chance that the mass of cells that you started out as would ever have left the test tube. The choice is not whether to make a baby a boy or a girl, it's choosing whether you want your offspring to be male or female. There isn't technically a sex change, it's [simply] choosing to implant a viable embryo of a desired gender rather than one at random (as in natural fertilization). Now this is all the more disturbing from the pro-life camp, because to actually make this choice multiple embryos have to be fertilized and incubated to a certain point, at which time all but one are disposed of. From the perspective that life starts at conception, you're killing off several dozen (maybe even hundreds, depending on the scale of the incubation project) "unborn children". I personally see this argument as being very stupid, but there are a lot of people who see it this way.
As for "sex change" operations; these are only half-truths. You don't actually turn a man into a woman through any operation in any way other than cosmetic; the genetic structure is preserved in its entirety and all reproductive functions are permanently lost. A man who undergoes a sex-change operation is still a man (from a cellular sense and in many ways a hormonal sense as well) and vice-versa, despite what proponents of the procedure would have one believe. It's basic biology; we can't do full-scale genetic replacement (nor would we want to) nor can we reproduce the different configurations of organs (between male and female) as they develop naturally over the course of aging. The whole argument about legalizing it/making it illegal is more a legislated morality issue than a scientific one.
EDIT: My thoughts on the whole messing with nature business are mixed too; [no one hit me for this] the whole Women's Rights movement (as in freedoms, specifically the freedom for a woman to control her own body) has pretty much f***ed the natural order anyway. So from that standpoint, why not throw in the towel. At the same time, I don't really trust the institutions that are making these services available to do as good a job as mother nature (and besides, it really defeats the purpose of sex, something that in truth should never have left the realm of reproduction to begin with), and I really don't like the idea of "test tube babies" because of that.