So what you're saying is the South would have kept on using slaves instead of machines?
Sure, feed house clothe, and take care of hundreds of slaves, and animals, instead of a tractor. Did you forget plowing, and harvesting, and cleaning, had to be done by INDIVIDUALS until the advent of the internal combustion engine?
After the engines came, just what use would slaves have been? Do you still use a slide rule to do math? Do you ride a horse to work? Times change. Slavery would have passed soon anyway.
Who is to say that slaves wouldn’t have been kept to run the machines? By your logic, if tech advances would lead to less slaves then the cotton gin should have ushered in the end of slavery.