I don't believe there is a convincing argument to be made that the Southern states would have ratified the Constitution had it freed slaves (assuming it could have purchased them which is a hell of an assumption given the bankrupt Confederation). Hell for that matter that might have defeated it in New York since areas of that state had as high a concentration of slaves as any area of the nation.
It barely passed there as it was.
I do not need convincing of Lincoln's greatness all I have to do is read some of the garbage posted here by the Lincolnhaters such as the latest "Lincoln was Gay" absurdity. But I would not place him above Washington in that regard.
The South, especially Georgia, South and Carolina, would have never seceded at a time when the settlers living there were under the possible threat of constant warfare against native tribes.
Most of this talk was bluff, on their part.