That's usually how it starts.
But power corrupts...
It's not has easy has people think to go loco with eugenics. You have to be a totalitarian state with a strong police force to force people.
Were that it were that simple. Consider that people with sickle cell disease are resistant to malaria. So do you breed out sickle cell? Do you just breed it out in people living where malaria is rare, and allow it to remain in places where malaria is common?
If we were able to do large scale eugenics then it would be possible to eliminate malaria by eliminating Mosquitoes so this question is null and void.
We need to stop cowardly and take this issue by the horns. No more of this stupid "OMG HOLOCAUST" or a vision of totalitarian state where normal humans are inferior. That isn't going on happen.