That's fair. I hedged on Plato because he states that, while its pattern may exist in the stars, the Republic is not a place that can ever be realized on Earth. i don't think "The Laws", which, being for the real world, is much more restrained, includes similar ideas about eugenics.
The other examples you bring up-- and Aristotle could in some measure be added to it-- show what an exception and great man Hippocrates must have been to reject what was standard in his culture.
But it's no gratuitous dig at Darwin to say that Francis Galton (a brilliant man in his own right and the father of modern statistics) wa sthe father of modern eugenics and was inspired by Darwin, especially the Descent of Man, who had been inspired by Malthus.
My point is noty to hust hop up and down on Darwin. I think the relationship between the theory of natural selection and eugenics is one that should be investigated, just as the conservative consequences of the theory we all like that Freeper Arnhart writes about in his book, Darwinian Conservatism, should be investigated (speaking of which, there's a generally positive review of his book in the normally anti-Darwinism Weekly Standard by James Seaton, who I think is an awesome literary critic, here http://www.weeklystandard.com/Utilities/printer_preview.asp?idArticle=12157&R=EC5A29952 )
The reason why I say that is that some would say professor Arnhart is wrong in his interpretation of Darwin, and Galton was right, and I'm interested in which is correct.
Eugenics is pretty much the opposite of natural selection. Nature has her own criteria for what survives and breeds. Our deliberate choices suit our own purposes, but they're not necessarily going to result in something that can survive nature's tests. For example, many of our agricultural products are somewhat fragile, and wouldn't prevail in a natural state. In particular, Hitler's preference for only Aryan stock, had he succeeded, would have resulted in an impoverishment of the gene pool, which in nature is usually a bad choice for the long haul.
As for Arnhart, we had a thread a while ago on his work. I agree that Darwin's work is inherently conservative (but then we'd be haggling about definitions). To shortcut that, if you think Adam Smith's work is something that conservatives should embrace, then the same reasoning goes for Darwin's work. The survival and flourishing of enterprises in an unplanned economy is analogous to the activities of species in nature. It's arguable that Darwin was influenced by Smith's thinking. Both are products of the Enlightenment, as is the American Revolution itself. The knee-jerk rejection of Darwin (and of almost all scientific thinking) that I see on this website is -- to me -- the antithesis of conservatism (defined as Founding Father-style thinking about politics and economics).