Could eugenics work?
DefinitionFirst let's define work as "create a society which is more like the society someone might want". Eugenics is the effort to increase the frequency in a human population of genes useful for a purpose and decrease the frequency of genes harmful to that purpose.
PracticalityThe answer is yes. Thousands years of selective animal and plant breeding has shown that you can alter the gene frequency in a population and achieve desired results. There is no physical difficulty in applying the same methods to human populations, other than potential resistance by the subjects. Obviously humans are better at preventing breeding by direction rather than as they like than dogs are. Of course morally most people have more problems forcing two people to breed or not breed than they have with two horses or wheat plants.
There are limitations on the usefulness of eugenics.
Firstly the effect you want to create must be possible by changing individual humans, even if you're changing a lot of them. Changing genetics will not directly make a society more democratic, so eugenics prevent or abolish dictatorships. It might however change behaviour patterns of people to promote or diminish democratic values, if those values are heritable.
Secondly the quality to be changed must be heritable, although it need not be entirely heritable. Heritability is quantifiable and equals the proportion of variance of a trait in a population that is due to heredity. For instance height is about 80% heritable. If you have a group all of whom have the genetics equal in effect on height their actual heights will vary by about 20% as much as the general population. The more heritable a trait is the more eugenics can be used to alter it. If a trait is only say, 20% heritable you will only be able to change 20% of the variation in the trait at best. Not that heritability talks about the variation in the trait not the trait itself. You can't increase height by 80% because heritability is 80%. You can change it by (at most) 80% of how much it varies. So if humans varied in height from 1m to 2.2 height varies by +/- 120 cm so at most you could change height by 96 cm. In practice that you couldn't change height that much for various reasons.
Thirdly you must be able to measure that trait well enough to guide eugenic decisions. Height is fairly easy to quantify, but suppose you wanted to breed for "niceness". How would you quantify it well enough to make a reproductive decision? Perfect measurement is necessary, but the less accurate the measurement the harder it will be make changes. I will define "proxy usefulness" (u) as the proportion of the variance in a trait that is indicated by the proxy. So instances with the same proxy rating the actual value of the trait will variance will by (1-u) * general trait variance. So for instance if you can measure height very accurately you might have a .99 proxy usefulness for height. That means that the variation in actual height from the height you record is .01 of the variation in height.
A trait high in heritability and with a good proxy to measure it by can be increased over time by eugenic means.
Fourthly eugenics will only work if a way to change reproductive decisions in a particular way. If you can't change who gets born or not born you can't use eugenics, which leads on to the next subject.
MoralityThat leads to the question, should eugenics be used, and if so by what means and for what ends?
Let's deal with means first. Changing people's decisions about whether to breed is one set of means, technological means to alter the genetics of offspring are another. Let's deal with the former first. There are fundamentally 3 ways of changing a person's actions, force, reward and moral pressure.
Every attempt to use force to achieve eugenic ends has been abusive by definition and has the results you would expect from an abusive system. Those who want to put abusive systems in place tend to want to abuse, rather than solve the real problems of human beings. Therefore they are careless in their pursuit of any aims of actual value. Fundamentally a human being owns themselves, and therefore you have no right to control their reproductive system any more than you have a right to control their vocal chords. It should be noted as well that the Nazis extremely abusive in pursuing their goals and extremely vague about what those goals were. Defining what an Aryan is isn't easy. At least it isn't if you ignore all the actual science and history and make up a mythical ethnicity and call it 'Aryan'. Their efforts to eliminate mental disability were particularly clumsy because they refused to use the best proxies (which of course showed Ashkenazi Jews as smarter than Germans or anyone else).
Rewards are far preferable to force as a means of persuasion, provided the means of reward was not gained by force. This is for the same reason that wages are preferable to slavery as a means of getting cotton picked. Everyone has the right to make decisions about their own body. Everyone else has the right to offer them benefits for using it in ways the offerer would prefer. There is nothing inherently immoral about telling someone "You have a heritable trait that would make society worse if passed on, I will offer you these resources if you don't pass on those genes.". Neither is it immoral to say "I think you have heritable traits that would benefit society, you can have some resources if you breed.". It will be up to the owners of those resources to decide whether it is worth it to achieve eugenic goals.
Moral pressure is simply someone stating that they believe that doing something, or not doing it, is right or wrong. It is simply the expression of an opinion about the appropriateness of an action. If done without manipulation or deception there is no moral problems with this.
Thanks to technology selecting who should (not) breed and with who is only one eugenics method. Potential future individuals can be genetically selected or even improved before birth. An embryo found to have genes that are not beneficial can be terminated, in the case of in vitro fertilisation this can happen before implantation. This is already done with genes for serious genetic problems, but could be expanded to terminate all embryos that have genes for low IQ, or alcoholism. You can even choose to implant only those embryos that have the genes you want. This is not genetic engineering, no genes are being implanted in the embryo, they are only examined and used to determine if the embryo goes to term.
Provided you believe, as I do, that a clump of cells is not a human being then there is no moral problem in terminating it.
All these of course deal with the morality of the means, rather than the morality of the eugenic goals themselves.
Firstly of course the goals should be well-defined and refer to actual things that exist, not for instance the a mythical connection to some supposed past master race. Secondly the goals should actually make people's lives better. For example you could increase the general level of cognitive ability by eugenic means. Cognitive ability seems to have a good proxy in the form of IQ. It helps achieve improvements like better productivity, greater understand of phenomena and lower levels of violence. Other goals might be the reduction of harmful behaviours like addiction, which might have a genetic component.
Some people have claimed that eugenics would lead to problems of inbreeding, but that is unlikely to be a problem. Inbreeding became a problem with sub-species that were very intensively bred for particular traits. In dogs inbreeding became a real problem after the invention of "dog shows" that bred very intensively for very specific traits. When dogs were bred for more general traits like usefulness in sheep herding or in particular sorts of hunting inbreeding was not a serious problem. Additionally the populations they bred from were much smaller than the current human population. Even assuming that people will mainly breed within their own race* these races have hundreds of millions of members. Even if only the most desirable 1% bred (and that would be an extreme use of eugenics) there would still be enough diversity in that population to avoid inbreeding.
* Yes race is a valid genetic category of humans. Sorry if this is controversial but it's not to people who actually notice facts.