Problems with Eugenics
Problem 1: Eugenics requires accurate genetic research. Eugenics policies will give researchers and their backers an incentive to fudge data to make their relatives look superior. For example, the eugenicists of the early 20th century fudged data in order to keep out people we can now recognize as assets.
Problem 2: In order for eugenics to work, it is not only necessary for mental abilities to be genetic, it is necessary for them to vary smoothly depending on genes. That is, if two alleles produce higher IQ, combining them must be even better. That is not necessarily the case. It's possible for the heterozygous phenotype to be superior to either homozygous phenotype.
Problem 3: There are always trade-offs. Improving long-term memory and analytic ability may come at the expense of being able to recall what color the sky is on my^H^H one's planet.
Problem 4: Why isn't everybody a genius? If evolution works faster than expected, you would expect IQs to rise until the genes get into rough territory or trade-offs start becoming important.
I was reminded by the news that the Chinese government is considering making an attempt at eugenics.