Further to my previous post, my friend Wolfboy wrote this in the comments:
I also detect a leftover whiff of eugenics in this line of thought the idea that people who are bad represent a taint we need to clear from the gene pool. That seems to be in conflict with modern understanding of how genes work. I may be wrong here, but my understanding was that modern research showed that genes get turned on and off by environmental stimuli. If thats the case then any genetic predisposition to be an awful person is better handled by stopping it from being triggered (by looking after people better in general) than by trying to breed it out.
Eugenics. That is presumably why the original inquiry was about the prevalence of sterilize-bad-parents views specifically in the atheist / rationalist community. Eugenics, the idea of breeding humans for qualities like intelligence or athletic performance, was proposed by Francis Galton as a practical application of the theories of his cousin Charles Darwin. Darwin himself went along with the idea, although never enthusiastically, and with reservations about the social justice implications. The support it enjoyed for the next seventy-odd years came from places all along the left-right political spectrum, but almost entirely from the atheist-materialist side of the religious divide. That is quite possibly the basis for the (otherwise absurd) notion that the Nazis were a scientific and rationalistic bunch.
The Nazis showed the world what it would take to actually implement a eugenics programme, and since then the idea has been anathema among people of conscience. And rightly so, but when a problematic idea or practice becomes unthinkable within a culture, it doesnt get cut out cleanly. Not only will we not do this any more, people decide, we wont even go near it. The classic example (see Steven Pinkers The Better Angels of Our Nature, and yes, I know I cite that book a lot) is the odd little superstitions that have grown up around knives in European culture, such as not eating with them. Europeans used to use big sharp knives for all sorts of things, notably settling arguments. In Māori culture there are several prohibitions, like never sit on a table, which put together underline the point that people are not food. And in modern political discourse, ever since World War II people have been unduly chary of applying genetic science to Homo sapiens.
Sometimes it goes beyond chariness. Everyone knows everyone here being an actually rather select corner of the academosphere that all that selfish-genery and sociobiology and what not was long ago decisively refuted by honest left-leaning scientists like Stephen J. Gould and Richard Lewontin. Im afraid this is the same kind of fact as the fact that evolution and global warming are both fantasies of pinko atheists and any moment now honest God-fearing scientists will announce that theyre abandoning both. Gould and Lewontins fellow biologist and leftist Robert Trivers considers them both hopelessly dishonest. I havent read all the works he cites, but I remember reading Goulds The Pandas Thumb (which includes a critique of Richard Dawkins The Selfish Gene) and then immediately afterwards the second edition of The Selfish Gene (which includes a response to The Pandas Thumb), because of the stark contrast between them. Dawkins understood and answered Gould; Gould did not answer or understand Dawkins.
The abhorrent conclusion that people with disabilities (say) ought to be sterilized does not follow solely from the premise that many disabilities are inherited genetically. You also have to take the moral stance that disabled people are a nuisance which ought to be eliminated. Without that, its genetic is just as readily framed as grounds for compassion. The neoliberal attitude which we leftists have to fight today is not Get them out of the gene pool, its Anyone can overcome their disabilities by sheer willpower, so if you need to ask for help it means youre too lazy to deserve it. Well, you cant overcome a genetic condition by sheer willpower. Not permanently, anyway. You can overcome it for a day, sometimes, but itll be back tomorrow. Somehow that always seems to be harder to understand when its a mental condition. Acknowledging the reality of genetics would help the Lefts cause, not harm it.
Having hopefully addressed some of the underlying concerns, let me now deal with what Wolfboy actually said. Yes, genes do what they do in concert with the environment. DNA is, after all, just another molecule. Its special because it gets copied and persists through time, not because it has any unusual power to make things happen. But thats true of the DNA of every species on Earth, not just human DNA. And people have successfully used eugenic principles on dozens of animals and hundreds of plants. Changing the genes while keeping the environment constant will achieve just as much as vice versa. Some people at this point appeal to something called epigenetics, which I gather boils down to the claim that other things besides DNA get passed down the generations. I dont know how good science that is, but it doesnt affect the logic of eugenics, which vets the breeding population for anything that gets passed down, DNA or not.
So why would humans be different from any other species? The obvious answer is culture. We have it, and animals dont, right? Doesnt that override the effects of genes or something? Well, no, it doesnt. Personality runs in families, but not adopted families. My father is much more like the birth-family we met seven years ago than the adoptive family he grew up with. Nor is it true that other animals dont have culture, in the sense of behaviours passed down by imitation. One classic experiment successfully enculturated a group of young rhesus monkeys, normally a jumpy, belligerent species, with the more laid-back attitudes of the stump-tailed monkeys they were raised with. I gather the offspring of that group have carried on the new tradition. Whats different about humans is not culture but cultural variation. That, I suspect, is driven by language, which allows ideas to mix and match the way sexual reproduction does for genes. And that is very relevant indeed to the question of eugenics.
Most human inherited traits are not controlled by just one gene. A few are; if you have two copies of the gene for red hair, youll have red hair. But most, including intelligence and personality, are the sum of hundreds of different genes, each one of which has only a tiny effect. Now that doesnt by itself rule out eugenics. Lets suppose that sheep-herding ability in dogs is similarly polygenic, which as far as I know it is; mating good sheepdogs with good sheepdogs will still, over generations, accumulate good sheep-herding genes in one pile and give you better and better sheepdogs. The key point, however, is over generations. A dog can give birth to or sire a litter of puppies when it is less than a year old itself. Even given the fattiest nutrition and the most neglectful social environment, humans seldom get that far in under thirteen years. A human breeding programme would therefore take centuries to achieve measurable results by which time cultural change would have wiped out the programmes original goals.
All of which is assuming you could get the programme going in the first place. Eugenics also requires something else: you have to be able to control your subjects matings. Humans can unlock doors, open gates, dismantle fences, and above all they can cooperate with humans who share their goals and deceive humans who dont. And humans, like the yellow-eyed penguin, typically mate in private. You would be reduced to having to trust people to stick to the sexual norms you imposed on them. Which, well good luck with that.