I just realized something while re-reading your last post - we're falling into the false choice fallacy. It's inaccurate to describe American politics in the 1850s as either pro-slavery or abolition. There was a third position - containment of slavery. It's wrong to describe Lincoln in 1858 or '60 as an abolitionist. Both times he ran on a policy of containment. Containment was the more popular policy in the North than was abolition. I can accept that most abolitionists were motivated by humanitarian concerns if we understand that abolitionists were a small minority of voters.