You can't kill off the lower end of society. Something else will just take its place and become the new low end of society. Anyways history tells us the lower end of society existed during the reformation and enlightenment, directly contradicting your opinion:
https://brewminate.com/the-growth-of-literacy-in-western-europe-from-1500-to-1800/ The link suggests that only the rich could understand coherent arguments as they were the ones able to afford education, and only when education was opened to lower classes was when lower classes were able to understand coherent arguments. Indeed this is natural selection by helping upper classes and hurting lower classes. But it is not natural selection by killing lower classes, no that is a different argument. If that were the case, then there would be no need to open education to lower classes like Maria Theresa did. By your assertion this lower class that Maria Theresa cared for is already dead due to natural selection in medieval Europe.