Technology doesn’t make slavery obsolete, it just makes your slaves more efficient.
There had always been abolitionists who were against slavery simply because they thought it was immoral, not because they thought slaves weren’t needed anymore.
There had always been abolitionists who were against slavery simply because they thought it was immoral, not because they thought slaves weren’t needed anymore.
The economic problem with slavery is that you're paying for absolutely everything for a slave - their food, housing, healthcare, and more. And if they ever get sick, injured, or whatever else then you're also paying for that. And that's after you pay a huge lump sum up front to purchase them in the first place. In the US a run of the mill slave cost about the same as a house, and it continued to track that price oddly closely.
The industrial revolution created a wide availability of cheap hourly laborers where the person hiring paid only their wages, and had no obligation for any of their expenses. People utilizing this labor suddenly not only had morality on their side, but even had an economic edge over those still clinging onto slavery.
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Another relevant point I think is that cognitive dissonance also tends to kick in when something is lucrative. For instance I think Aristotle's work, Politics, is amazingly insightful and informative. Yet his defense of slavery was not only the weakest part of his work, by far, but basically just garbage. Unlike his other arguments which clearly started from first principles and worked their way forward, it's clear with slavery that he started with an assumption that he wanted to be true, and concocted an argument going backwards from there.
Incidentally, he also predicted the end of slavery with an industrial revolution, some 2500 years ago: "For if every instrument could accomplish its own work, obeying or anticipating the will of others, like the statues of Daedalus, or the tripods of Hephaestus, which, says the poet, 'Of their own accord entered the assembly of the Gods.' If, in like manner, the shuttle would weave and the plectrum touch the lyre without a hand to guide them, chief workmen would not want servants, nor masters slaves." [1]