I think they're talking about social darwinism. The idea that "survival of the fittest" can be naively applied to politics is a pretty easy way to convince people to commit genocide.
It appears you're right. However, I find it puzzling that it's mentioned here, since the gulf between "there are some genetic differences between the sexes" and "let's attempt to improve the human gene pool by murdering any group we find displeasing" is so great that they barely have any relationship at all.
Given that procreation requires one man and one woman to participate, it's going to be really hard to practice eugenics based on genetic differences between the sexes.
Sex-selective abortion is not eugenics. Nobody with even the most cursory understanding of human reproduction thinks that you'll permanently alter the gene pool by selecting one sex over another. This is totally unrelated, and I'm rather sad that I managed to get not one but two replies bringing it up, as if it were somehow relevant. The quality of this discussion is just astonishingly bad.
Beside selective abortion and embryo selection, it's already possible to derive gametes of both kinds from stem cells of arbitrary sex in mice, and it will most likely be possible to do the same with human cells soon.
Mice that descend from two males or two females have already been created in the lab.
You still need wombs, but they can be grafted and will probably be farmed from stem cells in the future too.
It's not about murdering people. The problem is, if you support policies that disadvantage people based on their genetics, you can gradually dehumanize those people. The (real) disadvantages of that outweigh the (supposed) advantages.
But if you are disadvantaging people that have objectively inferior genetics? Do you actually lose anything? Otherwise, are those people taking advantage of medical advances that prevent their deficiencies from being fatal?
Celiacs, for instance, seem to be a group that in previous generations succumbed to their condition, if not directly than indirectly because of general unfitness.
To be honest, as a survivor of childhood lymphoma, I ought to be dead, had I been born even 25 years earlier. I question whether my genetics have enough offsetting benefits to counter that predisposition to life-threatening cancer for any of my offspring.
Advanced medical care is part of the environment in a first-world country now. I'm sure a fish would think us genetically inferior for our dependence on air to live, but we don't see it that way. A dependence on advanced medical care is ultimately no different. Assuming civilization doesn't collapse, I'd expect various dependencies on medical treatment to gradually arise in the population, but there's nothing objectively wrong with that.
OK, but the gulf between that and "there is some genetic differences between the sexes" is still so large that you'd need a powerful telescope to see from one to the other.
As much as I disagree with your overall viewpoints, I'll agree on this one you have here. For a lot of individuals, the gap that you mention is huge such as to not have an immediate, explicit effect, and for one particular reason:
Something as simple as validating and completely "accepting" the notion that "there is[sic] some genetic differences between the sexes" requires individuals to throw out entire swathes of subsequent ideas/notions/etc, if we were to be logical about things. I.e. You now have "Men and women are equal but ..." or "Men and women are equal except when...", instead of the pure and logically consistent "Men and women are equal".
If you ask me, the entire thing (sex-differences topic) is starting to smell full of tiny errors and corner-cases. Perhaps we're on the verge of a paradigm shift happening once people clarify their ideas, without exceptions and acceptable-errors:
Equality isn't about people being literally identical. Nobody actually believes that. There are troubling facts like how men as a rule have a really hard time becoming pregnant that nobody denies.
Equality is about equal treatment. It's about judging the individual on their own merits, not some group they happen to belong to. "Men and women are equal" doesn't mean women are equally muscular and men can have babies. It means that when writing a law, selecting an employee, or counting a vote, you don't change your approach based on whether the person is a man or a woman.
There is nothing wrong with saying, for example, most of our warehouse workers are men because more men are able to do the heavy lifting required. There's nothing unequal about that. What equality demands is that you never say, I will not consider you for a warehouse job, regardless of your actual strength, because you are a woman and all women are too weak for it.
https://en.wikipedia.org/wiki/Social_Darwinism