The Late Midshipman Peter Preston would like a word with you.
Seriously though, genetic tailoring has the potential to solve more problems than it creates
if access to the techniques is widely distributed among the population. I'm willing to bet tall money that it won't be.
If there's one thing that's pretty universal in this world, it's the desire of the wealthy and powerful to insure their offspring don't have to cope with pesky level playing fields against the great unwashed masses. Those elites will want to horde such an advance among the smallest number of themselves possible, for as long as possible, and a lot of harm could result. If there's a small uber elite immune to disease, they might conclude that investing in medical and pharmaceutical research is an unnecessary investment of resources that could generate better returns elsewhere. These supers might decide that lesser beings really shouldn't have a say in their destiny because, without dispute, the elites' judgement and intelligence are superior; best keep all the decisions to themselves.
So, unless genetic tailoring is so cheap, and so widely available that anybody can do it, there are
a lot of scenarios in which it goes sideways