Vietcong said:
If you're talking about early eugenics, up until about 1930, it has no scientific validation today, because it failed even to distinguish heritable traits from environmental traits. (For example, it equated black race with lower intelligence.) This failure eventually lead to its association with state-sponsored discriminatory policies, by extension Naziism and after WW2, it gradually lost public favor. Its only effect was to transform Eurocentric prejudices into scientifically justified practices. Also, after 1957, with the discovery of DNA structure, genetic research shifted from selective breeding to direct manipulation of genes.
Genetics has advanced considerably since then, so that we are better able to gauge not only what is heritable, but also how to manipulate it. We now know that you can't apply one simple policy of selective breeding and necessarily hope to weed out some trait. In some ways, eugenics already exists, but in the form of non-coersive means, such as genetic testing and counseling.
IMO, the only effective way to remove undesirable genetic traits from the population is to directly manipulate germ line cells, which is a technology that is in infancy right now. Coersive selective breeding is bound to fail, not only because it's a violation of personal rights, but also because it's not guaranteed to work for every trait even when applied properly.