Lerone Bennett has been trashing Lincoln for many years.
I give great credit to Lincoln's attempts at abolition. He was more farsighted than most.
From a carpeted, centrally heated campus office, the issue of slavery is cut-and-dried moral issue. Slavery was wrong, and we should have ended it. Racism was bad, and we shouldn't have been that way, etc. But it's not so simple.
For one thing, what about property rights? Slaves were property, and freeing slaves with the stroke of a pen meant depriving slave owner's of property. Suppose they next decided to declare farmland common property? Lincoln was attracted to the idea of compensation to slaveholders.
Also, slaves were dependent on slave owners. How do you arrange for a multitude,newly free, to provide for itself? This explains the appeal repatriation.
Export agriculture required labor. Did Southern landowners have the means to pay wage-laborers? Was there a commercial infrastructure that would have ensured sufficient cash on hand.
Was Lincoln racist? Probably, but who wasn't? Who isn't today?
Unrelated to slavery, but important were European powers ready and waiting for the US to fracture into bite-sized chunks.
Lincoln had a lot on his plate back then.