Reminds me of Bill Clinton and "don't ask, don't tell."
Anyone with a lick of sense knew he was lying about his intentions from the get-go.
As another poster mentioned, the South since the days of Calhoun also resented protective tariffs on northern manufactured goods, because little of that revenue went to the South, while they had to bear the brunt of it due to a lack of local manufacturing.
While Lincoln was guilty of a bait and switch in many ways on the slavery issue (and the Emancipation Proclamation a stupid move that changed the public perception of the war from a patriotic war to preserve the Union to a massive loss of life for the Abolitionist's pet moral cause), there's also the fact that the South's action of firing on Ft. Sumter rather than attempting to peacefully petition for secession was an incredibly stupid move. After Sumter, the Union could claim the moral high ground of fighting a defensive war.