Despite what we've been told, the real reason behind the British banning of the slave trade is more economics and less Christian-inspired morality. The following is a brilliant passage (found on page 53 and 54 in the second edition revised) from C.L.R. James' classic book, The Black Jacobins:
It was the growth of San Domingo that was decisive. Pitt [William, "the Younger"] found that some 50 percent of the slaves imported into the British islands were sold to the French colonies. It was the British slave-trade, therefore, which was increasing French colonial produce and putting the European market into French hands. Britain was cutting its own throat. And even the profits from this export were likely not to last. Already a few years before the slave merchants had failed for £700,000 in a year. The French, seeking to provide their own slaves, were encroaching in Africa and increasing their share of the trade every year. Why should they continue to buy from Britain? Holland and Spain were doing the same. By 1786 Pitt, a disciple of Adam Smith, had seen the light clearly. He asked Wilberforce to undertake the campaign. Wilberforce represented the important division of Yorkshire, he had a great reputation, all the humanity, justice, stain on national character, etc., etc., would sound well coming from him. Pitt was in a hurry- it was important to bring the trade to a complete stop quickly and suddenly. The French had neither the capital nor the organization to make good the deficiency at once and he would ruin San Domingo at a stroke. In 1787 he warned Wilberforce that if he did not bring the motion in, somebody else would, and in 1788 he informed the Cabinet that he would not stay in it with those who opposed. Pitt was fairly certain of success in England. With truly British nerve he tried to persuade the European Governments to abolish the trade on the score of inhumanity. The French Government's negotiations had been to "compliment us and to keep us quiet and in good humour." The Dutch, less polite, gave a more abrupt negative. But here a great stroke of luck befell Pitt. France was then stirring with pre-revolutionary attacks on all obvious abuses, and one year after the Abolitionist Society had been formed in Britain, a group of Liberals in France, Brissot, Mirabeau, Pétion, Condorcet, Abbé Grégoire, all the great names of the first years of the revolution, followed the British example and formed a society, the Friends of the Negro. The leading spirit was Brissot, a journalist who had seen slavery in the United States. The society aimed at the abolition of slavery, published a journal, agitated. This suited the British down to the ground. Clarkson went to Paris, to stimulate "the slumbering energies" of the society, gave it money, supplied France with British anti-slavery propaganda. Despite the names that were to become so famous and a large membership, we must beware of thinking that the Friends of the Negro represented a force. The colonists took them seriously, the maritime bourgeoisie did not. It was the French Revolution which, with unexpected swiftness, would drag theses eloquent Frenchmen out of the stimulating excitement of philanthropic propaganda and put them face to face with economic reality.