Slate's biotechnology columnist William Saletan has suggested that there really is a "slippery slope" in bioethics -- at least for designer babies. He points out that parents have moved from screening embryos which will certainly have terrible and incurable diseases at birth to screening them for genes which might possibly predispose a person to a curable disease late in life. Some clinics urge screening to prevent not just the disease but "cancer predisposition syndrome". The idea is that no child should be required to go through life burdened by the fear of developing cancer at some stage later in life.

A survey by the Genetics and Public Policy Center has found that of the American IVF clinics which offer pre-implantation genetic diagnosis, 28% have used it to target genes which do not strike until adulthood. And 42% have used it for non-medical sex selection. "If PGD were evil, it would be easy to head off such abuses by banning it," writes Saletan. "But it's not. PGD prevents hellish diseases. In those cases, you have to say yes. And once you start saying yes, it's hard to say no. That's why they call it a slippery slope," write Saletan.