In 1776, a group of states wanted to break away from their Union, the "United Kingdom." They outlined some principles based on natural law which stated that governments should rule by the consent of the governed.
In 1861, a group of states wanted to break away from their Union, the "United States." The operated under the false assumption that the founding principles cited by the United States in leaving the United Kingdom would be respected when States wished to leave that Union.
Again, the confederates were true to the principle that founded this nation, it is the Union that failed to respect their right to leave.
You can wrap it in whatever flowery language you want, but it is the Union which rebelled against this nation's founding charter, not the Confederates.
If the Union argument was true, we would all still be British. It is not a strawman, it is a direct extension of your moral argument. If people don't have a right to leave, then the United States didn't have a right to leave either.
You have a dichotomy that you simply refuse to face.
The south was in a state of pique with the election of Lincoln and spontaneously chose to rebel against the new leader. There was no negotiation, no compromise, no appeal to the rule of law. The south's first option was war. If you can find commonality there then you are an army of one.
the Union which rebelled against this nation's founding charter, not the Confederates.
You have a reality that you simply refuse to face.