Fire Memes for Traitor Haters

Ok, that makes sense. I don't agree that you were clearly arguing that until this moment; I was, in fact, very confused as to what you were saying. But perhaps you're right that I'm misinterpreting the quote. I would argue, however, that social dominance and slavery are not too distant from each other. A big part of the justification that slavers used to salve their consciences was that blacks were naturally inferior to whites, therefore it was only natural that this state of affairs would end in slavery. Lincoln's aping of that logic in an era where a significant number of people used it to justify slavery might not, as you suggest, mean that he thought slavery was inevitable (as the slavers did). But it certainly muddies the waters.

I will concede this point, however; because it's not possible to get into his head at the moment he said those words and see precisely what he meant by them, the issue is muddy enough that he could have meant simply that there would necessarily be first and second class citizens in a mixed country, and not that this condition would necessarily lead to slavery. That being said, it doesn't detract much from the rest of my point, which was, as KevonLooney said, that the union was not at the outset particularly interested in outlawing slavery.

Edit: also, this quote was pre-war, not post-war. He said it in 1858.