The following thoughts pertain most directly to genetic engineering on human germ line cells, and are less applicable to the genetic modification to mature cells for smart therapies or to the genetic modification on plants and animals.
I was having a discussion last weekend when I was criticizing someone for not being prepared for success. Later we started talking about science. I was talking to him about genetic engineering and how it is an incredibly exciting, and an incredibly terrifying time in Science. I was asked to explain, and essentially I told him that it boiled down to the fact that the world and the field of science and of genetics are not prepared for success. Here is essentially what I told him with a little elaboration to clarify my meaning and a little background to give context.
When most people think of eugenics they think of the holocaust. More recently people would point to genocides in Yugoslavia or Darfur. When others think of eugenics, they think of the eugenics laws that were actively enforced all across the United States, and remained in effect in some places into the 70s. Few people hear eugenics and think about amniocenteses. In a very sad case of irony, the biggest moral victory for eugenics has been carried out in the United States by Jewish populations - the Ashkenazi Jews, specifically.
In addition to being much more likely to have very high IQ than the average population, Ashkenazi Jews are also tremendously more likely to be afflicted by Tay-Sachs, Canavan, familial dysautonomia, and cystic fibrosis, in addition to a few other less notable conditions. Because of the high frequency of these conditions, there has been a huge push over the last several decades to do prenatal testing for genetic abnormalities. This has resulted in a near total elimination of babies being born with severe birth defects, because of aborted pregnancies. In defending this practice, I have rhetorically asked if these are "lives worth living." I was appalled to learn that some of the first people to use that argument to justify continuing some lives while eliminating others were the Nazis. The slogan of part of their eugenics movement "Lebensunwertes Leben" translates to "life unworthy of life".
A sad reality is that in an effort to eliminate suffering by aborting certain pregnancies, we make judgements about the inferiority of specific genes. In some cases, it seems quite straightforward, but when we allow ourselves to make these judgements, it becomes unclear where the line is drawn. If we begin to make judgements that certain genes are more or less desirable than others, is it not a logical conclusion that some people are innately better or worse than other people. And if it is not possible to make these value judgements about people, is it not immoral to abort pregnancies based on these judgements.
If you think that it is not possible to make value judgements, then I would challenge you to explain whether or not it makes sense to seek treatments/cures for genetic conditions that are "no better or worse" than the alternative.
As we have more and more success with genetic engineering, we will have the potential to eliminate enormous amounts of suffering, but it is inevitable that the lines between disease and normal variation will be blurred. What happens when we eliminate variation on the "autism spectrum"? At what point does small stature become a disease? If you want to link things to single genes, I would remind you that sex is determined by a single gene on the y chromosome, and I don't think anyone would call being a particular sex a disease.
This is a difficult question. If you think the answers are easy, I would challenge you to think harder.
It seems straight forward on the extremes. Most people have an issue with the concept of designer babies. Most people also have an issue with NOT treating disease. But there is a major tradeoff that must be considered. By using genetic engineering (on human genomes) we are accepting that some genes are superior to others. Who should get to decide when that trade-off is acceptable. This is just a little food for thought. I look forward to comments or questions.