Lincoln was not perfectly enlightened by today’s standards neither is it fair to call Jefferson Davis a depraved human being, but it was the Confederacy who admitted that their regime was founded upon a cornerstone of slavery.
As one reads the speeches and letters of Confederate leaders during the war, it becomes apparent that they certainly didn't believe their main reason for fighting was to preserve slavery. The key issue was Southern independence, not slavery. However, the primary purpose of the federal invasion was always to destroy Southern independence and to force the seceded states back into the Union .
It was the Radical Republicans, much like the liberal democrats today, who used Southern blacks as a "voting base" and taught these modern day liberals everything they know: race baiting, big governmental politics, class warfare, etc.
When victory was clear, the North "used" Southern blacks most likely because they believe them to be inferior. You know that whole line of thought, "let's give them something, because we need 'em!" By the way, where is my mule!!