My understanding, from vaguely remembered school lessons, is that some conservatives tried to
use Darwin as a theoretical justification for social hierarchies, and for not helping the poor and letting "natural selection" pick the best. And, in some cases, even went as far as proposing
eugenic actions, such as rendering some people sterile (the poor or the handicapped) to prevent them from "polluting" the gene pool. Since these have since gained a bad reputation by being associated with the Nazis, it has given Darwin a bad name, for reasons that had nothing to do with him, or of course the validity of his theory.
Which bad reputation is now being re-used by ultra-conservatives to shed doubts on said theory. Ironic, isn't it?