well, what about a recessive allele that doesnt cause problems in the first generation but does in subsequent? What about co-dependent deadly / devastating gene expressions between newly added genes that pop up after 2 people with these co-active genes expressing like a hundred years from now? look, given what i studied and why, i would never say we should forever abstain from gene editing technology. BUT, we have to hold those who conduct genetic modification experiments to the absolute highest ethical and engineering standards. It is akin to the level of power given by atomic science, maybe even more. one can be sure that the powers of a God would include the power of the atom and the power of the gene near the top of the list.
Many of the really bad mutations are embryonic-lethal, which is why a surprisingly high proportion of pregnancies "don't take" or end in miscarriage.
I just wanted to push back a bit on the idea that medicine is badly "breaking" evolution by keeping people alive.