Perhaps part of the reason is that applying "selective breeding" to humans takes on a sinister tone, for at least two very good historical reasons. The first and most obvious is Nazism, but even if you regarded that as merely co-opting the principle for malicious ends, you still have the problem that eugenics was, from the very beginning, tied up in issues of class and race. It's difficult to see how to overcome that, because the other point of eugenics is that it claimed to be able to identify the desirable and undesirable elements based on external judgement, ie what a person looks like and how their life has transpired.