Hayek spends much of the first chapter arguing that bringing science to social questions has done little to bring insight. I already gave my general critique of Hayek as an ideologue in the previous post; here I want to focus on the nature of social science, and what I think Hayek gets right and wrong.
The biggest difference between natural science and social science is that natural science is more about discovery while social science is more about testing. Yes, natural and social scientists both make discoveries and they both test hypotheses, but human experience provides us plenty of ideas about social issues, and in some sense most social ideas are right within a certain domain of applicability. You don't need a double-blinded, properly-controlled, statistically rigorous study to know that standardized tests cannot tell you the entirety of a person's abilities, that humans have biases, that people often manage to rise above their prejudices, that people also fall short of their ideals, and that small changes in policy can have large or small effects in difference circumstances. As basic ideas, I think that casual observation of the world is sufficient support for all of them.
What social science can do at its best is answer questions like "When? Under what circumstances?" Social science can take us from "People have many biases, but they don't always control our behavior" to "Unconscious biases measured by this instrument have demonstrable effects in these settings but not those other settings." Social science can take us from "Sometimes policy changes matter, sometimes they don't" to "Raising the minimum wage by $0.25/hour from a baseline of $10/hour will have little effect on unemployment in a city with a high cost of living, but raising it by $2/hour in a locale with a low cost of living could have measurable effects on unemployment." Social science can take us from "Standardized tests don't tell you everything" to "Due to the narrow range of scores, the quantitative section of the GRE has little predictive power for PhD students in such-and-such field, but the relevant subject test explains X% of the variance in outcomes as measured by the following instrument."
So social science does not necessarily tell us much that we don't know on SOME level, but it tells us much about when our intuitions are valid and what their limitations are. Hayek, being interested in grand social questions and large "Ought" issues missed that, on some level. Ironically, though, Hayek's grandest hypothesis was falsifiable by casual observations (Western Europe is not a hellhole) without fancy statistical methods. He railed against a harder enemy than he was actually taken down by.
Natural science operates in domains where we have much less intuition, and much less prior experience from which to develop ideas. By the time we know enough to even frame a precise hypothesis about certain topics, we're often on our way to testing it. That's not to say that wrong ideas never take off, and that there's never a contest of hypotheses, but we're definitely operating in realms where we have (comparatively) fewer preconceptions to cling to.
Ironically, the people who most abuse social science are probably closest in practice to Hayek's approach to social questions. They run with a few findings that flatter their preconceptions and ignore contrary findings. They love "ought" more than "is." The only difference is that they flatter themselves with a pretense of empiricism, whereas he is openly critical of the excesses of empiricism.