I guess it's the future now. Here's an article about the first British baby to have been screened to not have the breast-cancer gene:

http://www.timesonline.co.uk/tol/news/uk/science/article5489548.ece

Summary: The father's sister, mother, and grandmother all had breast cancer. Using in-vitro fertilization, they were able to select an embryo that tested negative for a cancer gene that was causing the issue. If the baby had been born with the gene, she would have had an 80% chance of developing breast or ovarian cancer. Apparently, many women who test positive for the gene actually choose to have their breasts removed as a precaution.

That would have been a pretty shitty thing to pass on to a kid (and the kid's kids, grandkids, etc... assuming she survived.)

Obviously, this still raises the very serious question of designer babies and eugenics and such, but I don't see why this has to be an uncontrollable "slippery slope".