Doesn't light me off, but I would contend you're wrong in some of your assumptions. The Constitution was written "in order to form a more perfect Union". The original states united for the benefit of all. Whether or not it was written into the Constitution, I think there was an implicit understanding that states had the freedom to leave the Union if they felt their needs weren't being met. When the Constitution was first presented, it took nine states ratifying it for it to become effective, and any state that did not ratify it would not be part of this new union. Joining was a choice, which implies to me that leaving was a choice as well. The federal government was not designed to be a new monarchy, the very thing our FFs fought against. JMO, but that idea was born with Lincoln and the Civil War, and cemented with all the programs of FDR. Somewhere along the way of our history, the importance of state's rights, which were considered so valuable by our FFs, was forgotten. When the Constitutional Congress was formed, it involved representatives from every state, arguing for the rights of their states.
As for the Civil War being all about slavery, slavery was a big part, just not the only part. Not every Southerner who fought was a slave owner. Many Southerners simply fought for their homes. Many didn't believe the federal government had the right to dictate to them what was legal or illegal, be it slavery or anything else. Slavery was an evil institution, as I have previously stated, so understand my next comparison is about the idea of state rights, and not an actual comparison with slavery. Certain states have legalized marijuana despite it being illegal at the federal level. Do they have that right? Should they have that right? Or should federal law trump all and those states be punished? Again, not comparing slavery and legalized marijuana, just the idea that states should be allowed to make their own decisions.
I will never defend slavery. I'm glad it ended, even if it took a war to do it. But should the federal government be allowed to dictate to states what they can or cannot do? That was a huge part of the Civil War. Yes, it involved slavery, but overall, it was about whether or not the federal government had the right to force states into compliance. I don't think the Constitution allows for that, but Lincoln did it any way. This goes beyond slavery, but slavery always gets the headline, causing people to ignore all the underlying currents that were there.