The main thing to stop it is that we don’t know what genes to target to make super humans. If we did, someone would probably try. As perhaps they should, under some ethical systems.
Our relatively enlarged skulls are the result of a random mutation which gave some human/monkey, 2.4 million years ago, a diminutive, inferior jaw.(1) They would have looked like a freak at the time.
Russian scientists have bred dog-like creatures from wolves in the last century. In other words, they dont necessarily need to know which genes or pairings produce their desired results. Trial and error is sufficient. And I dont imagine every nation state is beholden to ethical standards. All they'd need is educated guesses, and then to select their desired traits from a litter of humans, euthanize the rest, and repeat. Hopefully this is not happening, as it makes me feel ill to think about.
Of course, human gestation and maturity has a longer turnover, but gene editing could produce accelerated results compared to classical breeding of traits.
1-https://www.nature.com/news/2004/040322/full/news040322-9.ht...
Foxes, not wolves: https://en.wikipedia.org/wiki/Domesticated_red_fox