From Destiny of Crime:
Eugenics, I suspect, was in reality a symptom of a growing impatience of intellectuals with the intractability of the human condition, with the fact that that Man was irredeemably imperfect. And this impatience grew because of a decline in the religious understanding of life (it was no coincidence that Chesterton, who saw so easily through the pretensions of eugenics, should have been firmly Christian, while none of his opponents was). In the 1920s sterilization of the unfit would do for humanity what psychopharmacology is now supposed to do: render it happy because perfect. No one with an understanding of Original Sin could believe such a thing – even if Original Sin is not based upon an actual historical truth.