How Social Darwinism Came About
In general, Herbert Spencer's positive reputation is as the coiner of "survival of fittest" and as the popularizer of Darwin. His negative reputation comes from his attempts to wed these ideas to society at large. Social Darwinism—the term generally applied to Spencer's sociological efforts—is often thought of as apologism for the wealthy, as it says those who are successful in society are those best-adapted to it, meaning the poor are less fit to survive in society. It's an understandable misconception, and other philosophers have advanced ideas more along those lines, but that wasn't really what Spencer was driving at.