It is written that slavery was not economic, Smaller farmers were already setting slaves loose prior to war. Have you never heard that history? I didn 't think you were one of those who were blind to the entire story
Slavery isn't picking cotton or whatever per se, rather it is forced labor. If a society is set up such that one group of people can be forced to do labor for another then it will happen. Where the labor is put to use (farming, factories, whatever) isn't the point but rather the point is that the labor is forced.
In the decades after the Civil War the country started to get more mechanized and factories in cities started to be the big thing. And people would go there because that life in the city was better than life in the country (which has been happening forever worldwide and continues to happen).
And eventually a movement started to reform the factories because people were working 12 hours a day, 7 days a week, in dangerous conditions, yadda, yadda, and there become a movement to improve the lot of people doing the labor.
But all that was when the labor was free to go where it wanted. What if that was happening where there was slavery? What kind of movement can there to be to improve the lot of people working in factories when the people working in factories are slaves? If slavery had continued then as the South became more mechanized the slaves would have been shifted from the fields to the factories.
As long as it was considered legit to have slave then people that could make money off of slavery would have slaves. Big plantations would eventually have been replaced with big factories and the slave labor would have shifted to the factories.
What incentive would the South have had to ever end slavery had it not been for the Civil War? Where would such a movement have begun and how would it have played out? I don't see how it was going to just die out on its own.
ETA: I don't see how it was going to just die out on its own ESPECIALLY considering that at the time it was spreading westward and that part of the tension between the North and the South was over whether westward territories becoming states should be allowed to toe have slavery or not. In the early 1860s the South was trying to SPREAD slavery in North America.