It is the height of hubris to presume that genetic engineering can produce better results than billions of years of evolution. Tweak our genes to improve our abilities in one area and you'll end up with unintended problems in another area. Hypothetically, would you take a 20% improvement in intelligence if it came with a 50% risk of schizophrenia?
Almost all of the genetic engineering done so far has been targeted toward a single goal: improving the productivity of domesticated plants and animals for agriculture. And while it has been successful in increasing food production, it has also produced breeds / strains that that are incapable of surviving without humans. There is no free lunch in genetic engineering.
The 50% with the schizophrenia will die or be locked up, and the rest will be smarter. So as a whole the species will become better with each iteration. Evolutionary selection will still march on, the source of improvements (natural variation or bio=engineered) is irrelevant.
Almost all of the genetic engineering done so far has been targeted toward a single goal: improving the productivity of domesticated plants and animals for agriculture. And while it has been successful in increasing food production, it has also produced breeds / strains that that are incapable of surviving without humans. There is no free lunch in genetic engineering.