The cotton gin was patented in 1794
Yes, but along with other innovations the writing was on the wall. Machines were cheaper and more efficient to use than slaves. Some realized this, other preferred to live in the past.
You would be hard-pressed to find a quote from southern leadership of the time indicating a belief that slavery was on its way out.
Just as politicians today will use the children or the poor for their appeal. They used what they thought would work, and at the time sticking with the current (conservative?) way of life is what they thought would work.
I will admit to being biased on the whole subject of that war. It is often brought up as a way to castigate the South and Southerners.
I lived in North Carolina in 1960 1963, at the beginning of the integration movement as a viable force. When we returned to Pennsylvania I continually heard about how Southerners tried to keep the Blacks down; this from the people of a town who refused to allow Blacks to live among them. At that time Crawford County, Pennsylvania was effectively segregated. There were no whites only or Blacks only signs, but there were exclusively white neighborhoods in fact, entire towns and schools as well as white only businesses.
I remember the school integration riots. Yes, federal troops were called in to Little Rock, but the worst riots and demonstrations were in Boston, Cleveland and other Northern cities, not the South. The Southern problems were mild in comparison. Even into the late 20th Century the KKK was more active in the North than in the South. To this day I hear the term nigger used derogatorily more often in the North.
Maybe I just have a dislike for the sanctimonious hypocrites.