Updated May 4
The taboo is overtly around the issue of coercion.
If you use the word “eugenics”, some people (as seen in this discussion) have a knee-jerk reaction, and automatically think “Nazis”. They think about targeting whole ethnic groups, or killing people, or forcible sterilisation.
However, I think some of the discomfort is really about the issue of people being encouraged to make their own rational choices, and exercise thought-out, responsible control over our lives and our bodies. That doesn’t sit too well with the majority, who view having children as something that just automatically and randomly “happens” to everyone.
The truth is, humans and other animals engage in large-scale selective breeding for fitness (including intelligence) all the time. It’s perfectly normal.
Some people get nervous when there is new technology involved, and explicitly stated selection:
Genetic Counselor: “Well, Mr. and Mrs. Smith, we have tested your (alleles, single nucleotide polymorphisms, scary scientific sounding stuff, etc), and I have some bad news. If you were to have a child, there would be a 50% chance of a devastating genetic disease, with nothing but misery and pain for said child, and for you.”
Couple (in unison): ”Bummer. We better not have any kids.”
Or it can go the other way:
Crackly Voice From Speaker: “Hi! Welcome to Jolly Jism Drive-Through Sperm Bank! May I take your order?”
Customer: “Yes, I’d like the Rocket Scientist with Olympic Champion… Healthy, tall, blond… Clean family history for cancer or mental illness.”
Crackly Voice From Speaker: “Excellent choice! Would you like a side order of artistic talent?”
Customer: “I’ll take the classical piano playing.”
Crackly Voice From Speaker: “Great, I’m whipping up your fresh hot sample right now! Please drive forward to the pickup window.”
And people do it in a more casual way constantly:
“Ewww, that person is stupid (or has any characteristic that repulses me), and I can barely stand to interact with them, so I certainly would never consent to having any kids with them.”
Some individuals are already pushed entirely out of the breeding pool, simply because they have characteristics which lead to being persistently rejected for sexual opportunities. They don’t have any “right” to produce children when they can’t find any willing mates.
Government force is already used to some extent, via the criminal justice system. One effect of imprisoning criminals is that it removes them from the breeding pool, either temporarily or permanently.
In the book, “Freakonomics”, the authors talked about the impact of abortion (specifically legalisation in the US) on subsequent crime rates. Maybe the reason why you weren’t mugged and killed in 1995, is because your assailant was aborted back in 1975.
I would also expect that the benefits expand, because he also won’t be using law enforcement or prison resources, or fathering another generation of low-functioning street criminals. And his sister, who was aborted a few years later, also won’t be contributing to the current generation of criminals, or to multi-generational poverty and welfare dependence, recycled by low-functioning people.
Some individuals may have an honest self-assessment that, “Me having children wouldn’t benefit anyone. It would be stupid and irresponsible, and a general, long-term disaster. So therefore, I won’t have any children.” This could range from medical history, to lacking financial resources, to simply having other priorities in life.
People who are considered conventionally “attractive” are really displaying good reproductive fitness. This can range from wide hips to get a large baby’s head through, all the way to financial status symbols. People with those characteristics will receive more attention and opportunities for mating, including with other people of high reproductive fitness.
People who get upset about all of this may just be worshipping fertility. Without caring about the suffering caused by low-functioning people producing children whom they are not equipped (mentally, behaviourally, financially) to raise in a decent manner. This includes some of those low-functioning parents actively inflicting the biological disaster by using alcohol and other drugs while pregnant.
A large portion of the people who are pumping out kids do so with exactly zero rational decision-making, self-control, or actions→consequences thinking.
And that is why the film, “Idiocracy” is gradually coming true. Mass collective bad behaviour leads to mass collective bad results, including on those of us who are not engaged in that bad behaviour. The alternative to eugenics is a default to dysgenics.