We already genetically engineer all our food, use modern medicine and technology, so I certainly see nothing wrong with using genetic engineering to better ourselves and improve our own quality of life if possible.
Protein supplements, vitamin supplements, medicine. These are all things which give us an advantage over what nature would naturally afford us, and you know what? We're better off because of it.
Human lifespans have continuously increased over the last century and we're still improving on those numbers.
If the genetic engineering has no side effects after rigorous testing, then I see no issue with making my child super strong, smart and agile. After all, as a parent I would only want what's best for them. Neither would I have any issues with using such technology to my own advantage.
Genetic engineering has several forms, today the only one that is not "invasive" if you will, is selection. That is taking the best of the best and only allowing that select few to continue to bread. In our society and for all of human existence people have been selecting their mates. This based on superior trates. Therefor the superior trates have sustained themselves over time whole inferior trates have gone away. I see no need to interfere.