I don't see anything wrong with genetic engineering humans per se, as long as it's done responsibly. In fact, it addresses a problem Darwin noticed a century and a half ago; namely, the fact that our species is busily trying to exempt itself from natural selection using technology. If we don't want to be practicing eugenics, and presumably we don't, genetic engineering offers us a morally tolerable way to continue to improve our species.

The important thing is to ensure that genetic engineering on humans is done in an equitable and responsible way. It would be very easy to end up with a society in which the rich are genetically engineered superhumans while the poor are locked in poverty and unable to escape. We should be planning how to avert that scenario, now, before it gets started. And of course, we will also need extensive testing regimens to make sure that we don't create a new generation of "thalidomide babies" through ill-considered gene tweaks.