It occurred to me last night that Darwin's Origin of Species was written just two years before the Civil War. In think this might mean something--not in the broad causal sense, but in the correlative sense. I don't have much background in intellectual history. But this is a question I hope to explore. What does natural selection mean for a bonded society?
The answer: It is a justification for slavery.
All good liberals hope that all good things go together. The local apogee of this thinking came in the 1990s, in which we hoped that increasing trade relations with China would give us cheaper tube socks and comfortable jobs in knowledge industries while letting the Chinese transform themselves from wretched peasants living in a tyrannical society into cheerful proletarians living in a happy democracy.
Well, we did get cheaper tube socks.
In the same way, liberals (and I'm using the term here in the broadest sense, to include everyone from John Stuart Mill to out-and-out social democrats) like to believe that more knowledge is better--that truth will somehow set us free. The history of social science should make us doubt that lesson. The recommended reading is Wikipedia's "Scientific Racism" article, which details how social science in a great many instances was used to justify existing power relations.
Before you say that social science has gotten "better" in that regard, think of exactly the kinds of things that critical theorists would mention, such as how psychometric theory is used by large organizations to make large organizations run better (e.g., ASVAB, the SAT) and the political consequences of that and how most research money comes from either the government generally or the military specifically. Yes, social science is "better," but I think that we should reflect on the fact that a good deal of what makes it better is likely to have come not from social science but from societal progress in general.
Returning to the main point: The argument is not that this was bad social science. In a lot of instances, it was the cutting-edge stuff that helped reify racial categorizations. (Think of IQ tests.) And it's hard for nonspecialists to determine the difference, anyway; if it were easy, then many fewer people would get tenure.
Natural selection obviously played a large role in all of this. The eugenics movement, the notion of the Victorian hierarchy of the races, and the general preoccupation with improving the "stock" of the "races" had real roots in (bad) readings of Darwin. This is different from the "Social Dariwnism" aspect of bad readings of Origins of the Species, by the way; this is simply reading in "natural facts" as social science. For the modern version, see the debate over The Bell Curve.
So when I say that natural selection is a justification for slavery, I mean really to say that we should not presume that there is an immediate and objectively understandable implication of the theory for social justice. Just the opposite. Such findings have no immediate implications for how we organize society. Regardless, we will read into them what we want to read, and the more powerful among us will see in these findings justifications for what they want to justify.
[Updated]: TNC has updated his original question, so I will update my answer. In a way, this is just a return to themes I have explored elsewhere, at greater length.
Ideas and innovations don't directly map onto the ways in which we view the social world. Ideas make politics, but not as they please; they do not make it under circumstances chosen by themselves, but under circumstances directly encountered, given and transmitted from the past.
This is why I oppose technological determinism. Politics and power always matter. We used to think that the Internet would help liberate the oppressed--remember the "Declaration of Independence of Cyberspace" and all the other techno-utopias of the 1990s?--but it turns out that the effect of the Internet is at best greatly curtailed by the type of government that you had when the Internet arrived. Chinese democracy is no nearer, and very possibly less near, now than in 1991. The causal weight of the reorganization of social networks is conditioned by the ability of the sovereign to coerce those networks into a form amenable to Leviathan.
In the same way, how are we to understand "the telegraph" shorn of its rootedness in actually existing societies? It clearly helped facilitate commerce and "progress" in a great many ways. On the other hand, it also helped facilitate imperial control of distant lands in greater detail. And, in the same way, we tend to think that radio was as much a boon to dictatorial governments as it was to democracy--which is to say, it was just a tool. (It is easy to imagine democracy without the radio, since it existed. But it is actually hard to imagine what a pre-20th century fascist state would have looked like. There's a reason we think it's significant that futurism fed fascism.)
Looking for moral progress is tough. It does exist! But it's telling that we can find just as much of it in Lincoln, who was after all a corporate lawyer, as in Gandhi, who thought that trains, telegraphs, and lawyers had ruined civilization.