Humans are a remarkably homogeneous species, with any two people, regardless of racial or ethnic group, being 99.9 percent identical at the genetic level. Still, the residual 0.1 percent translates to roughly three million spelling differences, with some conferring dramatically higher risk of Alzheimer's disease or breast cancer. Clearly, some DNA changes are unquestionably negative mutations, destroying the function of a crucial protein. But many of the common ones are likely to confer mixed blessings perhaps an increased risk of infection by one pathogen, but greater resistance to another. These are serious goals, not to be lightly dismissed.
Safety is, of course, a major concern.
Given the subtleties of human physiology, quick genetic fixes are likely to do more harm than good. But there will come a time when we can do such things safely, and it's not too soon to ask whether we should. If we cross that fateful threshold, I don't see how we can ever return. I part company from some of my colleagues here. While I'm strongly opposed to laws limiting scientific investigation, I would support a ban on modifying the human germline.