Not according to George Washington.
"The basis of our political systems is the right of the people to make and to alter their constitutions of government. But the Constitution which at any time exists, till changed by an explicit and authentic act of the whole people, is sacredly obligatory upon all."
George Washington, July, 1796
The Constitution contains a conflict resolution system -- the anendment process. The secessionists ignored that because they knew democratic and lawful processes did not serve their ends. That they could be defended today is just grotesque.
It is also a grotesque misreading (or failure to read) of the history to say they had morality or right on their side.
They were called damned traitors at the time, and they were damned traitors.
I'm not sure gnorance is an excuse.
Walt