Klinghoffer is confusing Haeckel’s “scientific” Darwinism with Charles Darwin:

Many studies of the origin of National Socialism claim that the vlkisch and proto-Nazi movement arose largely as a reaction to the materialistic ideas of nineteenth-century science and especially to the naturalistic philosophy of Ernst Haeckel and the German Monist League. Using hitherto unexplored material, Daniel Gasman calls this generalization into question. Arguing that the importance of science has been relatively neglected in accounts of the intellectual origins of Nazism, he attempts to show that Haeckel’s “scientific” Darwinism, and his movement, the German Monist League, were proto-Nazi in character.

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See:

From Haeckel to Hitler:
The Anatomy of a Controversy

IN BEN STEIN’S DOCUMENTARY FILM Expelled, the erstwhile game-show host and financial columnist attempted to link Darwin to Hitler and thereby condemn the scientific theory of evolution by association with the political theory of National Socialism. The film failed, fortunately, and was thoroughly panned by the critics. But in the cultural brouhaha stirred by the film’s release and subsequent disappearance from the big screen, not enough attention has been paid to whether or not there was a historical connection between the social Darwinists of the 19th century with the National Socialists of the 20th century. It turns out that there is, through the personage of the German biologist Ernst Haeckel; but a new biography of Haeckel, published shortly after Stein exited stage left, claims to rehabilitate Haeckel by disconnecting him from German social Darwinism, and thereby exonerating evolutionary theory. Unfortunately this new biography does no such thing, for in the end we must be true to the historical facts.
Robert J. Richard’s The Tragic Sense of Life: Ernst Haeckel and the Struggle Over Evolutionary Thought2 promises to rescue Haeckel from a century and a half of disparaging assessments of his biology, and above all undertakes a refutation of the more recent and widely held belief that he was instrumental in formulating the basic tenets of Nazi ideology. The common understanding among historians about the connection between Haeckel and Hitler is this: Adolf Hitler (b. 1889) came of age during the decade and a half following the publication in 1899 of Ernst Haeckel’s Riddle of the Universe, a runaway best seller that over the next two or three decades sold more copies internationally than the Bible and profoundly shaped the consciousness of the modern world. Haeckel’s book imparted a rigid Social Darwinist message purportedly derived from science: politics is applied biology, the Jews were an inferior race compared with the Aryans, Christianity was a religion of weakness, and that eugenic action was necessary to protect the racial composition of society….

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