[patall]

There is a fundamental difference. Natural Selection works on an individual basis, everyone tries to maximize the amount of his or her DNA in the world. In eugenics (and to a lesser degree in social selection) someone else (or the group) decides that his or her DNA should not be inheritet. Basically capitalism vs. communism.

[brute]

In sexual selection there is also someone else (i.e. the group of females in a peacock population) that decide whose DNA should not be inherited. And sexual selection is considered a part of natural selection. So your argument does not hold.

Wikipedia: Sexual selection is a mode of natural selection where members of one biological sex choose mates of the other sex to mate with

https://en.wikipedia.org/wiki/Sexual_selection

I could even argue the same thing for natural selection itself. When a predator kills an animal, he decides that the DNA of that animal should not be spread further in the future.

[TheOtherHobbes]

Humans are only "fundamentally different" in that we have alpha castes as well as alpha individuals.

It's not unusual for animal alphas to monopolise/deny mating opportunities. Eugenics is the same evolutionary invention taken up a level.

Ironically, this means proponents are acting just like animals.