Here's a picture of Obama Sr and his Irish wife. Yep he sure looks like he's only 6% Negro. He also was a dyed in the wool socialist/Marxist. The apple didn't fall down far from the tree, either the mother tree or the father tree.
I'll tell you why Lincoln was right then and is right now in another post.
Those were Obama’s numbers from his own bio info.(3 per cent negroid by the way. Arabic traders is kind of generic, since they may have darker or lighter pigments depending on where they hailed from, some of them might have been mixed)
Kamala Harris’s mom was a Dark Indian from India. Her father was from Irish stock with some mixed blood thrown in. It doesn’t take much genetic variant to make the skin of some descendents look dark.
There are plenty of places in the US where minorities and whites get along especially newer churches.
I believe Lincoln was wrong in his views at least during the 1862 meeting that you cite. His emancipation proclamation might have been argued to be designed to put more pressure on the south by arousing in the blacks a greater desire to be free and to try to create insurrection within the southern borders. Lincoln however knew that after war’s end that slavery was never again going to be an American institution nor did he try to preserve it. Whatever and however he may have felt about blacks, he knew that slavery was a pernicious sickness in any civilization trying to call itself great.