The greatest dangers will be religious fanatics or radical enviromentalists that will not see such persons as persons but should hate or fear of others decide of the lives of one?
The corresponding ethical issues of genetic engineering are complex and deserve serious attention in what may be a relatively short interval before these capabilities become a reality. Each society will decide for itself where to draw the line on human genetic engineering, but we can expect a diversity of perspectives. Almost certainly, some countries will allow genetic engineering, thereby opening the door for global elites who can afford to travel for access to reproductive technology. As with most technologies, the rich and powerful will be the first beneficiaries. Eventually, though, I believe many countries will not only legalize human genetic engineering, but even make it a (voluntary) part of their national healthcare systems. The alternative would be inequality of a kind never before experienced in human history. I believe that in the end all will benefit from such universal program, guaranteeing everyone being born healthy, fit and intelligent.
Another question what should be the limit of the genetic engineering, and I in my opinion we should only modify non-positional traits. A positional good benefits you only because others lack it. Height may be an advantage in men, but if everybody were three inches taller, nobody would be better off. Attractiveness may be another example of a positional good. A gain for one person implies a relative loss for others. I would contrast that with a trait like health. Your life is better when you are healthy, even if others are also healthy. Cognitive enhancements are a complex topic, but they have aspects that are intrinsically valuable. It is good if we can understand the world better.