A question I have not read about is, "Why did the British (in our case) select Africans as the slave of choice? Could they have selected some other group: Aboriginals, South Asians, Arabs...?
I am guessing there are two, maybe three reasons:
The first is that it was convenient to obtain slaves from Africa. You remember the triangular trade map from American history? Ships left the American Colonies with rum (before cotton became a big crop) and unloaded the liquor in England. Then the ships traveled south to Africa where they picked up slaves. Then to the Caribbean colonies to unload the slaves who would be used on cane plantations. Molasses was loaded up and taken to New York and Boston. The molasses was made into rum which was shipped to England.
The second is that there were slave sellers on the African Coast. The English didn't have to hunt down slaves; Africans did that chore for them, in exchange for desired goods.
Why did the Africans sell their own kind into slavery? Well, for one -- they didn't see much of what happened to slaves. The trip west or east (Arab slave traders) was a one way trip. Two, people are willing enough to sell out strangers, and for the most part, the Africans who were sold into slavery were strangers to the sellers. Europeans were not the first people to obtain and trade in African slaves. Arab nations obtain slaves along the north and west coast of Africa. [Among the last states to abolish slavery were Saudi Arabia and Yemen, which abolished slavery in 1962 under pressure from Britain; Oman in 1970; and Mauritania in 1905, 1981, and again in August 2007.]
I don't know whether 17th and 18th century British society considered Africans sub-human or not. I get the impression the British of the time tended to consider everyone who wasn't upper-class British to be sub human. Snobs.
Again, you would have to sell me on "all slavery is equally bad" before I could accept this. — ZhouBoTong
We are debating degrees of suffering here, not whether there was suffering. Was being a Greek slave/tutor in Rome no worse than being sent to the mines? Granted: The mines were obviously worse. Slaves died at a high rates in (some) mines, or wished they were dead, maybe. But bear in mind that an educated Greek didn't start out life as a slave or as a tutor. He probably became a slave because he failed in business, was swindled, or was captured during a war. His family was enslaved as well. In the Empire, a person could be transposed from top of the heap to bottom of the heap in short order. The transition from a man of importance to slavery (even if in a post where one could use one's knowledge) involved a radical adjustment in status.
Granted again: What makes slavery bad is the kind of labor one is forced to perform. Gladiators might have had the worst labor--fighting to the death. Working in the mines was pretty bad. Agriculture? Long days, certainly -- but the agriculture of olive, grape, and grain growing (as well as garden farming) were not as horrible as cotton or cane farming. For one thing, vineyards require skill on the part of workers. The workers had to be happy enough to be careful about what they were doing.
Southern American and Caribbean slavery involved quite disagreeable working conditions. Romans had some very unpleasant work too--galley slaves, for instance, but nothing on the scale of the cotton industry. (At least, that is my impression.) Also, in the ancient world, no worker had a particularly easy life, because work was mostly manual. Slave or free, work was a lot of sweating labor.
Here's a clip from I Claudius, where Livia, Emperor Augustus's wife gives the gladiators a pep talk. She's very much against them using professional tricks to stay alive. In Robert Graves novel (based on Suetonius) Livia was chief conspirator (for whatever skullduggery was going to happen). She's a real nice person.