European slave traders were only concerned with one motive: profit. They were businessmen who were engaged in the business for a return on their investment. The slave trade was often discussed at London and Liverpool business clubs and social meetings as a means of making money. Nations which had no colonial interests, such as Belgium and Denmark, often engaged in the trace. The Brown brothers of Newport, Rhode Island operated the largest slave importation business in the U.S., although most of their ships docked at Charleston, S.C. They used the money from the trade to endow a university which they named for themselves: Brown University. One particular Joint Stock Company, (forerunners of the modern corporation) The Royal African Company, was organized for the sole purpose of engaging in the slave trade. John Newton, who later became an Anglican Minister and is famous for having written Amazing Grace served as captain of a slave trip for many years.
Perhaps the most graphic example of the attitude of slave merchants was the Zong affair. The Zong, a slavery with an inexperienced captain, overshot its intended port in Jamaca. Facing a loss for the voyage, the captain, one Luke Collingwood, on November 29, 1781, had the slaves thrown overboard en masse and filed a claim with the ships insurers for lost cargo. The applicable provision of the insurance policy read:
The insurer takes upon him the risk of the loss, capture, and death of slaves, or any other unavoidable accident to them: but natural death is always understood to be excepted: by natural death is meant, not only when it happens by disease or sickness, but also when the captive destroys himself through despair, which often happens: but when slaves are killed, or thrown into the sea in order to quell an insurrection on their part, then the insurers must answer.
When the insurance company refused to pay, Collingwood and company sued and won. The presiding Judge, Lord Mansfield, in his verdict expressed the feeling of most slave traders:
What is this claim that human people have been thrown overboard? This is a case of chattels or goods. Blacks are goods and property; it is madness to accuse these well-serving honourable men of murder. They acted out of necessity and in the most appropriate manner for the cause. The late Captain Collingwood acted in the interest of his ship to protect the safety of his crew. To question the judgement of an experienced well-travelled captain held in the highest regard is one of folly, especially when talking of slaves. The case is the same as if wood had been thrown overboard.
There was surely some amount of variation in how they felt, but it stands to reason that those who kept on with the business felt that it was an acceptable and perfectly moral thing to do. If they had thought it was evil, they surely could have found other ways to make a living.
The average slave trader probably did not really think of the slaves as real people. This was a time, of course, when racism was pervasive and perfectly acceptable in society. In fact, it is not a stretch to say that most Europeans believed in white supremacy. They felt that Africans were much inferior to them and that they did not, therefore, have the same sorts of rights that whtie people had. Because of this, they would not have thought that what they were doing was wrong any more than we think that a slaughterhouse worker is evil for killing animals.