There are good reasons to go to war and bad reasons to go to war. The south may have had a right to secede but it was for a wrong, immoral reason. In either way it’s a joke to think either side would have gotten along peacefully after this. Further the plantation system was dying in the face of industrialization and would have petered out and then what would have been the point of expensive to maintain slaves?
If the plantation system would have ended on its own, it should have been allowed to do so.