Clearly the moral argument against eugenics can dealt with by breeding for immoral people.
As an aside, I can't help but chuckle at how comically bad this "clarification" tweet is:
"I'm not saying I think eugenics is a good idea; I'm just casually throwing out there that it really could improve humanity"
to answer the OP:
no, Eugenics on humans isn't possible because there are too many around.
The one thing you need for Eugenics is a population you can screen for a trait and control their reproduction accordingly.
not a chance with billions of people in hundreds of countries.
The internet is a eugenics program that creates Untermenschen.
Clearly the moral argument against eugenics can dealt with by breeding for immoral people.
How does breeding people who can jump higher "improve humanity"?
If you need/want people to jump higher, breeding humans who jump higher would be an improvement. However, that was just a flip example given based on the history of eugenics in movies and culture. Look at it from another point of view: Is disease immunity an improvement? If you could make the world's population 25% more resistant to diseases that cost a lot to cure or alleviate, look at the money you could save the healthcare system.
And I don't think Dawkins is talking about breeding humans so much, as that is a long term trial and error project, and the one most people are familiar with through the Nazis and apocalyptic movies . I think he is referring to engineering humans which is happening already. In fact, many scientists believe modern human beings are a new species based on our ability to genetically modify ourselves and other life forms.
The issue with all the eugenics programs in movies and books is that all the "failures", and there are always a lot of them, are eliminated. That's where the moral issues mostly come from. You have a large population of "inferior" humans being killed which is a great opportunity for a movie/literary hero to step in, save the day, and show us the error of our ways.
That issue can be eliminated through genetic engineering. First off, there would be very few "failures" because the problems would be caught long before they became viable humans. Secondly, if your goal for example is to make the general population 25% more resistant to certain diseases, what few "failures" did occur wouldn't matter in the overall population. People would still get the disease, they would just be less likely.
The issue, as always, is what traits would be an improvement and who gets to decide? That might be solved by having a list of things science can improve and allowing each parent to select the ones important to them, or not choose any.
But Dawkins is correct, eugenics would work on humans.
No, no. You're making the same mistake Dawkins did, which is trying to force a redefinition of "eugenics" as just a completely interchangeable synonym for "directed breeding in general". It's not. Eugenics was invented as a social policy with a very specific goal in mind - the "improvement" of humans, not based on objectively better or more useful physical traits but ideologically (i.e., arbitrarily) chosen "desirable" ones. There is no stripping it of its sociological and political context; these are intrinsic.
Honestly, what is next - a dispassionate analysis of the positive and negative macroeconomic consequences of consolidating ghettos and interning their inhabitants in labor camps? "I'm not saying we should use concentration camps; I'm just making a point that there would be undeniable benefits in terms of reduced manufacturing costs, not to mention the immense savings on health care by disposing of ill worker-units rather than treating them while they're not producing".
You showed much more nuance and careful framing in this short explanation than Dawkins did in his tweet. His tweet boiled down to "Ackshually, eugenics could work!".
Dawkins is not an unintelligent man. Makes you think why he might post about such an inflammatory topic in such a careless way.
If the question is can we breed bigger people, then sure, eugenics can work. If the question is can we breed more intelligent people, then sure, eugenics can work.
If the question, however, is can we breed better people, then surely the jury is out until we firstly decide what would constitute better people, and secondly establish whether we can isolate those traits genetically.
You showed much more nuance and careful framing in this short explanation than Dawkins did in his tweet. His tweet boiled down to "Ackshually, eugenics could work!".
That post was 1,951 characters long. Dawkins had a limit of 280.