You don't really need to understand genetics very well to do eugenics see animal husbandry and except for certain dog breeds the unintended consequences of have proven to pretty manageable in animals (except in some breeds where targeting a certain appearance rather than temperament, physical ability or intelligence is the primary goal).

The difference is that with animal breeding you have a clear distinction between the people doing the breeding and the animals being bred. Humans breeding humans any attempt at being "scientific" is likely to collapse in the face of the resulting signaling games.

I mean look at the current state of social science, do you think it would somehow magically improve if eugenics were to be embraced? In fact, it's likely to get worse since the results of social science would then have even more significance.