You just confused Eugenics with Euthanasia which are completely different things. Eugenics is reproductive control on a very high level, and may go even as far

You just confused Eugenics with Euthanasia which are completely different things. Eugenics is reproductive control on a very high level, and may go even as far as governmental control on procreation. Aside the ethical problems with Eugenics there's also a problem raising from simple statistics: In which way shall it be decided who may procreate with whom and who not? Any kind of biased selection eventually leads to a drop in genetic diversity. However the smaller the genetic diversity the higher the chance for illnesses and defects to spread within the population. So if the ultimate goal is genetic diversity the only sound selection would be to make as much mix-and-matches as possible. Interestingly enough mitochondrial transplantation adds a little to genetic diversity, because it dissolves the meiosis relationship between female nuclear DNA and mitochondrial DNA.