There were at least two strains of anti-slavery thought, and it's necessary to differentiate them.

Probably the most familiar to us, though the least influential, were the out-and-out abolitionists. These made up a small minority of the Northern population and were heavily concentrated in New England. Their ideas, especially those favoring enfranchisement of and equality for freed slaves, were not widely popular before the war. However, they exercised an outsized influence through their public activities. Frederick Douglas, William Lloyd Garrison, Harriet Beecher Stowe, Ralph Waldo Emerson, and other authors, newspapermen, preachers, and speakers helped to keep the message in public discourse, and the South in a state of stirred-up agitation.

The other group, whom we'll call the anti-slavery faction, were motivated by a variety of factors - moral repulsion by slavery, belief in the corrupting nature of the institution, its negative effects on whites, and superiority of free labor in an economic sense. They were also less strident in their demands. They sought an eventual end to slavery, to be brought about by preventing its future spread. Above all, they wished to keep it out of the North, which after the Dred Scott decision began to seem in doubt. Anti-slavery voters almost always outnumbered the true abolitionists by a large margin.

These individuals were less certain of what to do with black people after the anticipated collapse of slavery. Blacks as jurors and voters made many of them uneasy. Lincoln, probably the chief anti-slavery politician, initially hoped to colonize the freedmen out of the United States, to set them up in central America or Africa and be rid of the whole problem. This naturally earned him the ire of the abolition faction. But, like his faction generally, the war and prolonged contact with slavery helped to radicalize Lincoln and push him to favor of abolition and citizenship.