Keep in mind that Eugenics fell into disfavor, it wasn't proven to not work.
It does work, there is no way for it not to work. The only way it could not work is if evolution and natural selection didn't work either. Traits are heritable.
IQ is highly heritable.
Criminality is even heritable.
Twin studies have shown that demeanor and interests are highly heritable. Far, far more of who we are and what we will do in life is determined by our genetics than anyone cares to accept.
People don't like the idea of
not being a blank slate, but instead being a slate with a lot of stuff already written before anyone even hands you the chalk.
Too bad, it's true.
And liberals are very, very good at realizing how dangerous it is to ignore ozone depletion, or carbon emissions, or deforestation, or soil erosion, or endangered species losing their habitats. They're also good at understanding evolution.
Liberals like to look at conservatives who bury their head in the sand about some or most of these issues and shake their head in disgust, "How can they not see the long term impact of us doing nothing about this issue?"
Yet, when it touches on our own species and the biological realities of it, liberals suddenly give conservatives a run for their money when it comes to denial of scientific reality and the long term implications of doing nothing about a trend, or even worse... doing things to make the trend even more damaging.
Nobody wants to live in the kind of society where the government is telling you you can't drive a certain type of car or that you have to limit your driving or get an emissions test or that by a certain date you must have switched to a newer car with better environmental impact. Yet, if everyone refuses to be willing to accept some sort of government intervention to control these things, our planet's climate may become irrevocably hostile to human life, and billions may die from our species and others. Cities may be lost to rising sea levels, etc.
Likewise, nobody wants to live in a society where the government tells you how many kids you can have, or where it takes certain people aside and sterilizes them because an understanding of heritability of traits is being utilized to maintain the health of the society/species. In fact, people don't even want to deal with the softest possible version of such policies, like government payments to incentivize certain people (like perhaps those on welfare or those with certain types of criminal records) to voluntarily be sterilized.
So in this case, both liberals and conservatives are burying their heads in the sand and pretending that you can create a civilization that effectively puts natural selection out on its ass, and then take no effort whatsoever to replace its effect - you can just let people breed willy nilly in an environment where massive amounts of calories are available even to those with the genes most threatening to a healthy, safe society. And somehow, it'll all just work out. We never need to do anything unpleasant, not even anything slightly unpleasant.
Yea, let's see how that works out for us.