The quote was fairly straightforward about his views, I don't see how they could be misconstrued, but hey maybe he was just "talking off the top of his head" and really didn't mean them to be taken in the same way that the socialists and eugenics advocates took them to mean!
I blame socialist politicians and other such "wormtongues"(think Lord of the Rings) for the misuse of science in order to bend society towards evil ends. The quote has often been used by those socialists and eugenics advocates as a justification for their insane views...whether or not Darwin was an Active advocate of eugenics or not. The language of the quote how-ever certainly sounds as though he had positive thoughts in regard to such 'cleansing' of the human species.
I understand your frustrations....most scientists are ethical, moral, and generally harmless folks. Yet not so nice governments and politicians use the fruits of science to enslave men. Christians know this to be true for they are aquainted with the moral evils to which men can sink and of the evil ends to which science can be made to serve.
If it were a matter of just pure research, Christians wouldn't give a fig leaf. In the early 1900's during the first battles concerning evolution and its teachings in the public schools, it wasn't merely evolution but a whole array of socialist policies advocated by Sanger et al that folks were concerned about. Evolution became a convenient bugaboo to attack because it represented in many folks minds
the linch pin core thought of leftist radicals who wanted to remake society into a secularist anti God state.
Mathemetics couldn't be made to attack a society's core values. Physics couldn't be bent to attack a society's core values. Chemistry could be made to attack a society's core values. I mean you don't have Christians protesting the teaching of physics and chemistry in the public schools, right? So maybe we're not so anti-science as you would figure?
Yet it was biology and evolution, the theories of which were seized upon by atheists and secular minded "reformers" with which to attempt drive a wedge between church and society? If questions of lifes origins could be used to destroy religious thought, then a society could be restructured out of the moral chaos such a loss morality would create!
Thus there is a moral battle between good and evil, a battle in which objective science, in light of true scientific methodology, should take no sides in! Unfortunately, science has been bent to serve evil purposes all to often in the last 300 years!