This notion was slowly creeping all across the continent. Though there were many Southerners defending slavery, there were also many who were souring on it.
Charles Dickens wrote a chapter on the issue.
Given the one way nature of this social repugnance, the trend was steadily moving towards universal abolition, but was being held back by the economic benefits of the system. Even so, support for it was eroding, and it would have eventually become frowned upon by the majorities in the South.
The Cotton gin had made it economically profitable, and the tractor would eventually be along to make it economically unprofitable. All it needed was time.
I concur with your entire assessment.