So genetic enhancement is too dangerous to be ethical because we haven't done enough human testing, and actually doing those tests would also be unethical?

Ethics are great, but ultimately the human race isn't the dominant species on the planet because of how incredibly ethical we are. If we want to actually have the benefits of an improved species, we also need to be willing to take the risks associated with that. A scientific revolution is not a tea party; people die whenever new methods of treatment emerge, every new discovery is ultimately used by people who don't understand it, and initial applications are always limited by cultural biases.

Human nature isn't going to change unless we change it, so why not do so now? There's no actual existential threat, especially since implementation is likely going to be very limited for the first few decades, so any failures will be instructive. With such a vast reward for fairly low risk, it would be an uncharacteristically poor judgment call for humanity to turn our backs on this technology.