Originally Posted by
Sar1n
Any kind of genetic engineering is inherently unpredictable. Even if we manage to completely map out the entire human genome and its interactions, it's impossible to predict how will it interact with future changes in environment. An adverse mutation can prove, under certain circumstances, beneficial, and there is no way to be sure that the mutation won't evolve further into something useful. Therefore any genetic engineering in humans, especially one that removes diversity from population, should be limited to cases where it removes something that has a very significant, possibly terminal impact of the quality of life of that person, for example Down's syndrome or SMA (spinal muscle atrophy).
Genetic engineering among crops or livestock is a different matter, many ethical concerns are irrelevant for those, but that's another topic entirely.