[Stammer]

Wouldn' eventually overtime the people who have been selectively breed will end up being so closely related that you'll see the same genetic problems you see in children born of incest?

Plus the biological diversity of the human race is what has kept us alive, because not every population is afflicted by certain diseases. Eugenics kills biological diversity leaving said population at greater risk for having horrible epidemics that would wipe enormous swatches of it's population out.