Growing up with Indiana Jones and the Temple of Doom as a favorite movie, I got the impression that slavery was all about capturing young able-bodied children for mine work. Roots sat on the head-end of my timeline but if I saw that I’d have additional prejudices about slavery. Most of us who have grown up inside the public school system and with mass media in the home may have similar preconceptions. That’s not a value judgment but a matter of fact.
Picture this: your village was attached, scorched-earth style, by a roving horde of Fu-Manchued Barbarians, and most of the men who bothered to fight back were killed or injured. There’s zero usable infrastructure within a twenty mile radius, and the nearest (friendly) village is 100 hundred miles away. By the way, you have no car, no horse, and no wagon—remember, those were destroyed. Why do you have a car, anyways? There’s no proper pavement system conceived yet.
In this scenario, your only hope is to walk 100 miles while (possibly) injured, with no money or food, hope that you don’t get jumped by roadside bandits, mauled by bears, or collapse from starvation. So you’re pretty desperate, and Head Fu-Manchued Barbarian knows this: he may be violent but he’s not an idiot, since people who are able to successfully plan and execute a thousand-man, thousand-mile hack-and-slash fest on horseback are by definition no idiot. What do you think he’d do? Killing you is an option but why waste energy and resources for little to no return? He could use a good cook, scullery maid, or blacksmith back home in Barbaria. Better yet, he knows Fellow Fu-Manchued Barbarian a few huts down who is more desperate for your expertise and is willing to part with some big denarii for your skill set. You, however, have no options besides death. Head Fu-Manchued Barbarian (as mentioned, he’s not an idiot) knows this, and despite the quivering, unsheathed sabre in his hand, he cools off for a few seconds to let his frontal lobe recharge. He makes you an offer. Enter slavery.
This is a very specific example, but it may have been the origin story for a lot of slavery throughout history. One has to arrive to a very unsavory but very strong inference that slavery was more for the benefit of the slave than the slaveholder. In this situation that you’re in, it’s kind of unavoidable, and again in this situation, launching all the “slavery is bad” arguments miss the point. It’s not slavery that’s the worse thing, it’s war, and slavery is an unfortunate result of it.
You can probably look up statistics for yourselves, but the fact that waning of slavery’s popularity or “usefulness” coincided suspiciously with the creeping flood of industrialization and legislative action. In other words, industrialization began to make slavery the less attractive option for cost/benefit purposes, and the political aspect piggybacked on the wave of cultural shift. A politician outlawing slavery when neither slaves nor slaveholders would want it outlawed would get laughed at and soundly thrashed, but if popular opinion shifts the opposite direction, a career bureaucrat stands to gain by making a show of creating laws and reaping the social currency of a movement that was already underway without their meddling. As incentives change, so goes the politician, but also the nature of the slaveowner. As slavery slowly became financially impractical, it may have been the case that the more cruelty-oriented of them held onto the institution and rent-seeked for government services—southern American slaveowners relied on state authorities to capture runaway slaves. Without the benefit of the state, the real profit-seekers would be relying on the sectors with time-saving technology, leaving the those that prefer cruelty over profits as the bulk of slaveholders. This makes it easier to create a case for slavery’s abolition and thus, in popular memory, we are left with the slaveholder as the cruel actor.