I just finished the book In Pursuit of the Gene by James Schwartz where he writes about Darwin's contributions to genetics.

Darwin and more notably his cousin Francis Galton embraced eugenics. In fact Galton coined the term, which means "good stock". From the late 1800's to the early 1900's most geneticists accepted eugenics as a good thing and it came in many different flavors. For example, Nobel winner Hermann Muller believed eugenics was only possible with communism, since capitalism does not promote "good" genes (his words).

Going back to Darwin, he didn't hold a lot of the same views many modern people have today about race and eugenics. He believed that his concepts of evolution justified the apparent differences of race. So I would argue that he himself justified racism and eugenics with his own concepts.

He [Darwin] was also convinced that evolution was progressive, and that the white races—especially the Europeans—were evolutionarily more advanced than the black races, thus establishing race differences and a racial hierarchy. Darwin's views on gender, too, were utterly conventional. He stated that the result of sexual selection is for men to be, “more courageous, pugnacious and energetic than woman [with] a more inventive genius.

Rose S. Darwin, race and gender. EMBO Reports. 2009;10(4):297-298. doi:10.1038/embor.2009.40.

Also if you're interested, Darwin's contribution to genetics outside the theory of evolution was misguided. He borrowed concepts from the Ancient Atomists (see Lucretius On the Nature of Things) and developed the theory where "genetic molecules" from all over the body collect in the gonads, which are then used to make a zygote. He with Galton tried to experimentally test this theory by connecting two different lines of purebred rabbits by their blood vessels, assuming the genetic molecules would pass from the blood of one rabbit to another. This experiment obviously failed and Darwin died without any resolution for the mechanism on the origin of the species. A few decades before his death, Mendel already documented his pea plant experiment which would provide a solid foundation for Darwin's theory. Mendel was unknown in academic circles until the late 1800's.

I'd like to add that the eugenics-related ideas and attitudes now associated with 'Darwinsim' did not actually originate with Darwin nor his cousin. A concise example can be found in personal notes, published posthumously of the famous physicist Sadi Carnot:

In some respects medicine is directly opposed to the will of nature, which tends to perpetuate the strongest and best of the species, and to abandon the delicate to a thousand forms of destruction. This is what occurs among animals and savage men. Only the most robust attain the adult age, and these only reproduce the species. Medicine and the aids of the social state prolong the lives of feeble creatures whose posterity is usually equally feeble.

Among the Spartans, barbarous regulations put an end to the existence of malformed infants, that the strength and beauty of the race might be preserved. Such regulations are antipathetic to our customs; nevertheless it might be desirable that we should devote ourselves to the preservation of the human race from the causes of weakness and degeneracy

A fairly typical 19th century 'Darwinist' view is expressed here, but it was written 30 years (give or take a few) before On the Origin of Species. These thoughts were already around at that time (and there's no reason to think Carnot was unique or first here, or even that he didn't get the idea from elsewhere - very little is known about him)

What Darwin's new theory of evolution was gets misstated a lot; Darwin did not propose the world was eons old, the geologists had done that already starting in the 18th century. Darwin did not come up with the idea of species being in a family-tree type relationship (Linnaeus), or that species evolved from common ancestors (Lamarck). What Darwin did was to come up with the idea of hereditary traits together with natural selection as the mechanism of evolution, and came up with a detailed theory with observations and arguments to support it, in "On the Origin of Species by Means of Natural Selection" - despite the second part of the title explicitly emphasizing what the big new idea is, it often gets missed.