Gender is not a disease," a Northwestern University fertility specialist recently told The Washington Post. "My job is to help people make healthy babies, not help people design their babies."

And yet, when affluent couples select the sex of their babies by using preimplantation genetic diagnosis (PGD) in connection with in vitro fertilization, they are in danger of treating gender like a disease.

PGD was developed to detect genetically transmitted diseases such as hemophilia and Tay-Sachs disease and to allow couples to destroy those "defective" embryos. Pro-life Christians shudder at the deliberate destruction of any embryo, but applying this search-and-destroy technique to sex selection adds a new and frightening dimension to reproductive technology: We are now seeing the intersection of old-fashioned eugenic ideology with the very American ethic of choice.

In the early decades of the 20th century, the eugenics movement flourished as high-minded moral reformers (including many evangelical Christians) sought to perfect society by purging it of "undesirables." People with disabilities or destructive habits were discouraged or banned from reproducing. One prominent evangelical crusader spoke of "the great and rapidly increasing army of idiots, insane, imbeciles, blind, deaf-mutes, epileptics, paralytics, the murderers, thieves, drunkards, and moral perverts" and called them "very poor material with which to subdue the world," and usher in the glad day when "all shall know the Lord." She suggested that there were "hundreds and thousands of men and women … to whom in the interests of future generations, some rigid law should say, 'Write this one childless.'"

The eugenics movement finally lost its last shred of credibility ...