‘but the noble and gentle people of the south would have arrived there eveuntally’
which explains why they were so gung-ho on expanding slavery to the western territories...
Change comes slowly to people, I am not sure at all that the mindset of all slave owners was to give up their slaves. The reality though was that slaves were very expensive, not just to purchase but to support. Each thing that allowed a slave owner to save on labor was leading to less slaves being needed. Some owners were turning against slavery for moral reasons- it became more and more common to give slaves their freedom. I have read many accounts of people inheriting slaves, and choosing to give them their freedom. There are also many accounts of people freeing slaves in their will.
I do believe slavery would have died out on its own, but the time frame- that is up for debate. I don’t have any idea if morals or the need for less labor would have led to it ending fairly quickly or over a long time frame. I know if I were a slave I would certainly not want to wait for freedom.