Cotton was extremely profitable and helped the North a good deal as they also had access to the crops and could transport it amongst other things. To be clear, everyone agrees that slavery is a bad thing and that it was the lure of more money that made taking care of slaves not being an actual responsibility so much as making profits grow?
On a side note, wasn't there a few thighs in the Cnfederate Constituion which banned even speaking about ending slavery and limiting states rights on the issue of masters wanting to free their slaves? That and the despotism may have gave Lincoln extra reason to believe the Southern leadership was looking for greater control over everyone beneath them, Black or White. Ahh, and then there are all the areas that were against secession....
Ahhh, and doing so would mean less wars. The Confederates might have tried claiming US Territories, empty out reservations, and, of course, expand South.