The ethics and practical ramifications of using genetic engineering to create the “perfect” baby while preventing the development of embryos the final form of which would be imperfect have been debated for many years. The engineering involved occurs in a laboratory during which female eggs are screened for flaws and matched with male sperm that has been processed to separate out imperfections, with the fertilized egg reinserted into the female through a process called “in vitro fertilization” (IVF), which is very expensive and physically uncomfortable for the female. IVF has become a very common practice, and ethical dilemmas surrounding its use have been few and muted. It is a standard manner by which couples experiencing difficulty conceiving are provided a helping-hand in the form of modern medical technology.
Questions arise, however, when the effort becomes oriented towards attempts at engineering the perfect baby rather than simply conceiving a baby. The IVF process would be fundamentally flawed if imperfect components of the equation were not extracted to the extent possible. Whether pregnancies should be terminated in the event diagnostic testing indicates a potential medical problem in the embryo, however, is an emotionally-charged issue for which no resolution is in sight.
The advantages to genetic engineering are well-known, and involve the increased likelihood of a baby being born with no physical deformities, which can involve extremely expensive medical bills for many years and a potentially diminished quality of life for the child. Disadvantages include the ethical principle of selectively “weeding-out” the imperfect and, as significantly, preventing the births of children who may very well turn out to be the next Stephen Hawking, capable of making major contributions to the sciences or to literature despite serious physical afflictions. This answer would be remiss, also, if it did not include reference to the religious considerations that are part of the debate regarding genetically-modified babies. For those who believe that conception is a matter best left to God, then manipulating the process by which babies are created is a moral sin.