Plenticide (eugenics, genocide, pesticides) : human civilization of the Modern era seems determined to get rid of all of its nearest and dearest , leaving just a tiny 'saving seed' of the most perfect and the purest of humanity to exist all alone in this vast lifeless Universe.
It just didn't make sense : for the more evidence that emerged that the universe was old, vast and empty the harder humanity, circa 1930, tried to eliminate most of what little life was confirmed to exist in the universe : that of Earth itself.
Perhaps, you might argue, they hoped to find lots of new companions from among the little green people kitted out in metallic scales and bearing two heads that would surely be found on places like Mars.
But does that wash ?
In a culture consumed with fears that "black" men, black because one drop of black blood was enough to define them as negro and not because they looked in anyway black, might marry their daughters and then perform unspeakable crimes of miscegenation ?
Could a species that regarded it as a serious crime for its members to marry other members of that same species if they looked at all different (the felony of miscegenation) and trying to kill off all other of the familiar lifeforms on planet Earth, ever find something in common with the unfamiliar lifeforms from planets with physical conditions so different from that of Earth ?
Not the ray guns would be blasting all those seductive little green women to death faster than you can say Buck Rogers or Flash Gordon.
Flash Gordon, a Yale educated WASP, didn't even truck with consorting with alien women from this planet (ie recent Catholic or Jewish immigrants to America) - so why expect him to indulge in miscegenation with aliens from other planets ?
No we can only account for this new emphasis on plenticide in the modern era by seeing it as the result of two simultaneous reactions combining.
One was a near universal 'revulsion inwards' reaction among educated humanity to science's 'natural history' revelations that the totality of reality and lifeforms was far far greater than ever imagined and far far more entangled together in complicated ways.
A revulsion against miscegenation in every sphere and in every dimension.
Living and marrying only within one's ethnicity and class seemed far more simple and predictable.
But this inwardness and sense of go-it-alone autarky seemed only realistically possible because other branches of science were, at the same time, claiming that below the surface complexity of reality, it was actually extremely simple and predictable and even controllable.
Scientific reductionism promised that all that now existed or could ever exist, Man could easily synthesize from the atoms of useless rocks, with the limitless energy of the splitting atom.
Not only did WASP males of circa 1930 now feel revulsed at the thought of having sex with their black female slaves, they also no longer needed the strong backs of black male slaves either, as machines had replaced them.
Neither was wanted or needed on this pure voyage into the progressive future.
Hence : Revulsion + Reductionism = Plenticide.