I guess you never heard of the American Colonization Society --- founded by James Madison when Lincoln was just a kid. The aim was to free slaves and fund a nation for them where they could live free. It did form the nation of Liberia. Neither Madison or Lincoln could see how freed slaves could ever reach full citizenship in the US when you considered the racial attitudes of the day. Were they wrong in that belief? Consider that it was 100 years after Lincoln died and all slaves were free before many blacks were even allowed to take a pee in the same toilet as a white.
Ask yourself the question. If you were black in 1860, would you have wanted to stay in the US, or would you have rather had your own nation?
You ask if I would have wanted to remain in the US in 1860, were I black. Yes, absolutely.