If it was about that, they would have made a case for secession before Congress prior to attacking Fort Sumter. Surely the right of revolution should only be invoked after at least making an effort at a compromise before attacking.
The domestic political processes of the United States, even when they amount to a civil war, are not binding on other states, however similar or dissimilar they be. I can imagine California would be prevented if they asked for independence today, but Scotland looked pretty much free to go if they'd wanted it recently.
The Civil War was not about some kind of ideal of decentralization and certainly was not about today's pining for city-states. It was mostly about slavery, with some esoteric political theory tacked on to the Confederate Constitution to save face.
Not exactly. Those who wanted out of that fairly free arrangement did not want others to get out of literal bondage. The freedom to oppress is not what I was talking about.