Lincoln, and I think most white Americans in the North, did not like or at least were embarassed by the existence of slavery in the South but Lincoln, correctly in my view, took the view that in normal circumstances the US government could not take action to end slavery.
Had the South not rebelled there would have been no way to legally end slavery other than by state action and the Planter class tended to have disproportionate influence on those.
So I wonder