Social Darwinism is of course, anti-Social in most cases, and anti-Darwinian in all cases.
But it is the way that Social Darwinism is anti-Darwinian that is interesting and bears on some of the controversies surrounding sociobiology.
All forms of Social Darwinism have historically been Larmarkian in origins. It is not simply that most Social Darwinists misunderstood Darwin but rather their speculations actually contradict Darwin's thinking on many core issues. There is no notion of "progress" (except in a very local way where a bird or a bee may adapt a specialization that makes it better at extracting pollen, for example) in Darwin; no progressive hierarchy of life, and certainly no hierarchy of civilization. The only measure of success in Darwin is reproductive success.
Now to those of you who oppose Social Darwinism, as I do, you might consider that Spenser and later Social Darwinists shared many of their views with Marx and Engels, and to a lesser extent Kropotkin. They all assume the same Larmarkian distortions of evolution, and apply those distortions to human history and biology. These are mistakes that sociobiologists, even when they make claims that are simplistic and reductionist, never make.
One of the best books that covers the application of evolutionary theories to human behavior is "Sense & Nonsense: evolutionary perspectives on human behaviour" by Kevin N. Laland and Gillian R. Brown. (Oxford). I would suggest that all leftest opposed to sociobiology on principle read it. The reason the book is good is that it gives a history of the controversy around these subjects along with giving a short precis of the theories themselves.
In that book the authors write,
"We can also see that, historically, certain ideas have tended to go together: a Lamarckian view of evolution, with species arranged on a ladder and a linear, progressive concept of change, perhaps inevitably engenders prejudice as some evolved forms must be regarded as more advanced, or 'higher', than others. Many of the inequitable views of human races indirectly resulted from this Lamarckian viewpoint. In contrast, the Darwinian conception of evolution stresses within-species variation and rejects the typological thinking that is inherent in racism. In addition to the role of natural selection modern Darwinism places considerable emphasis on chance events such as mutation and genetic drift. There is nothing about natural selection that supports a progression of populations towards an end goal or 'higher' state. In fact, the misrepresentation of evolution as progressive was so apparent to Darwin that in his notebooks he reminded himself to 'never say higher or lower', ... and evolutionary biologists now recognize that it is impossible to define non-arbitrary criteria by which progress in evolution can be measured.... As no variant can be regarded as more advanced than others, Darwinian evolution is inconsistent with racism and Social Darwinism. It is largely by distorting Darwinian thinking that evolution has been used to justify prejudice and inequality. Most of the negative features sometimes unfairly attributed to evolution, including prejudice, racism, sexism, genetic determinism, and Social Darwinism, do not come from Darwin but from others who twisted his theory."
I think that the most controversial thing I have to say here is that unfortunately Marx and Engels shared some of the Larmarckian prejudices in ways quite similar to Social Darwinists of the late 19th century. But I think that this does not harm their better insights.
Jerry