You are a little confused. Lincoln favored not letting any NEW states have slavery. He hoped the institution would wither like it did in the rest of the world. The fact that Lincoln was able to win the electoral college without a single slave state voting for him is what panicked the South, not whatever Lincoln actually proposed.
But for the South, they had an irrational fear that once the slaves were freed, they would seek revenge on their white masters, just like they did in Haiti.
When that didn't happen, and the North lost interest in Reconstruction, then people realized they looked pretty fucking silly trying to destroy the union so a few rich white people could own slaves.
That's when you started hearing shit over economic reasons and state's rights and other garbage when it was about... slavery.