Maintenance of slavery was not the main issue dividing North and South in 1860, expansion of slavery was. There was a big difference.
Sort of.
The ability for slaveowners to expand their empire (as Messpinola/et al keep insisting) had been there for some time, yet what happened? Nothing of significance. Slaves in the west were a rarity. Allmost all of the reasons for war seem to be driven more by fiery rhetoric than by a desire to actually carry slavery westward.
Now, understand that there's a huge difference between "not wanting" to do something, and "being prevented from" doing something. The latter makes you a second-class citizen in your own country. Once you've achieved that status, it's probably easy to start looking for other abuses (tariff, infrastructure investment, etc) and convince yourself that you've had enough.
Regardless, motivation for doing something has no bearing on whether or not the right to do so exists.