Darwin and his family (both the Darwins and the Wedgewoods) were 19th century liberals = 20th century conservatives. They believed in capitalism, markets, individual opportunity, individual responsibility, all that. They were passionately anti-slavery (Darwin nearly was thrown off or left the Beagle expedition twice due to arguments over slavery with the Tory captain, Fitzroy). Later in life Darwin was a fundraiser for the prosecution of Govenor Maury, who had brutalized and gratuitously killed thousands of native Jamaicans in putting down a revolt. Darwin, in The Descent of Man argued systematically and persuasively for "monogenism," and against the "polygenist" view -- which had originated among creationist anthropologists, btw, before evolution was a consideration -- that the races of man should be considered as separate species. In fact Darwin's work can arguably be considered the final and definitive nail in the coffin of polygenist anthropology (although there would be various attempts at revival over the years, the last being Carlton Coon in the 60's).
Was Darwin morally and ideologically perfect by late 20th century standards? No, certainly not. The assumption of biological superiority of white Europeans was pervasive in his time. It was the truly exceptional individual that even questioned it. Darwin sought and found tangible evidence of the unity of man in a thousand mundane facts, and brought them together in a systematic biological philosophy.
Darwin was certainly a cultural chauvanist. This is not entirely a bad thing, as conservatives know, and indeed Victorian England did acheive possibly the highest level political, economic and individual liberty of any society at the time. But there was, on Darwin's part, a certain self-satisfied upper-middle class comfort with liberal English civilization that made for a real shock when he came face to face with his first real "savages" living in their native state in Tierra del Fuego. This drove Darwin to wonder about what differences were biological and what cultural, but despite some areas of uncertainty, Darwin clearly believed that it was overwhelmingly conditions of existence, rather than biology, that accounted for the vast gulf he percieved between the civilized man and the savage.
In this respect Darwin was, for instance, very much less racist than Abraham Lincoln (who was Darwin's age, indeed born on the very same day). It is clear that Lincoln really did believe that blacks were inherently inferior to whites. Yet Lincoln's moral excellence lay in his conviction that, in spite of their alleged average inferiority, blacks should have the same rights as any other man and be afforded real opportunities to acheive all that was possible to them. Darwin, sans the racism, felt similarly, although his vision was to transform savages in to good Englishmen. He and Beagle captain Fitzroy together wrote a pamphlet extolling the accomplishments of English missionaries in lifting the morality, civility and material conditions of native peoples around the world. Even in later years Darwin occassionaly defended missionaries against their critics.
Just to give an idea of the passion of Darwin's feelings about slavery, here is a passage from his account of the Beagle voyage. This was added in a revision he made just after his good friend and mentor Charles Lyell published his book on the Antiquity of Man (if I am remembering this right). Lyell, following a think a trip to America, made some rather mild passing comment in his book that some slaves had good masters and a decent existence. Darwin was outraged by this comment, and poured that outrage into the following passage:
On the 19th of August we finally left the shores of Brazil. I thank God, I shall never again visit a slave-country. To this day, if I hear a distant scream, it recalls with painful vividness my feelings, when passing a house near Pernambuco, I heard the most pitiable moans, and could not but suspect that some poor slave was being tortured, yet knew that I was as powerless as a child even to remonstrate. I suspected that these moans were from a tortured slave, for I was told that this was the case in another instance. Near Rio de Janeiro I lived opposite to an old lady, who kept screws to crush the fingers of her female slaves. I have stayed in a house where a young household mulatto, daily and hourly, was reviled, beaten, and persecuted enough to break the spirit of the lowest animal. I have seen a little boy, six or seven years old, struck thrice with a horse-whip (before I could interfere) on his naked head, for having handed me a glass of water not quite clean; I saw his father tremble at a mere glance from his master's eye. These latter cruelties were witnessed by me in a Spanish colony, in which it has always been said, that slaves are better treated than by the Portuguese, English, or other European nations. I have seen at Rio de Janeiro a powerful negro afraid to ward off a blow directed, as he thought, at his face. I was present when a kind-hearted man was on the point of separating forever the men, women, and little children of a large number of families who had long lived together. I will not even allude to the many heart-sickening atrocities which I authentically heard of; -- nor would I have mentioned the above revolting details, had I not met with several people, so blinded by the constitutional gaiety of the negro as to speak of slavery as a tolerable evil. Such people have generally visited at the houses of the upper classes, where the domestic slaves are usually well treated, and they have not, like myself, lived amongst the lower classes. Such inquirers will ask slaves about their condition; they forget that the slave must indeed be dull, who does not calculate on the chance of his answer reaching his master's ears.
It is argued that self-interest will prevent excessive cruelty; as if self-interest protected our domestic animals, which are far less likely than degraded slaves, to stir up the rage of their savage masters. It is an argument long since protested against with noble feeling, and strikingly exemplified, by the ever-illustrious Humboldt. It is often attempted to palliate slavery by comparing the state of slaves with our poorer countrymen: if the misery of our poor be caused not by the laws of nature, but by our institutions, great is our sin; but how this bears on slavery, I cannot see; as well might the use of the thumb-screw be defended in one land, by showing that men in another land suffered from some dreadful disease. Those who look tenderly at the slave owner, and with a cold heart at the slave, never seem to put themselves into the position of the latter; what a cheerless prospect, with not even a hope of change! picture to yourself the chance, ever hanging over you, of your wife and your little children -- those objects which nature urges even the slave to call his own -- being torn from you and sold like beasts to the first bidder! And these deeds are done and palliated by men, who profess to love their neighbours as themselves, who believe in God, and pray that his Will be done on earth! It makes one's blood boil, yet heart tremble, to think that we Englishmen and our American descendants, with their boastful cry of liberty, have been and are so guilty: but it is a consolation to reflect, that we at least have made a greater sacrifice, than ever made by any nation, to expiate our sin.