Once again our debate has come full circle. The concept of unilateral state secession doesn't have to be supported in U.S. law. A state that has seceded is no longer bound by U.S. law.
Perhaps you would like to address the fact that there was nothing in English law that supported the right of a colony to exercise unilateral secession. From that perspective the colonists were nothing but filthy rebels who deserved to be ground into the dirt and forced back into submission just like Lincoln did in the South.
What you overlook is the fact that the colonists were victorious filthy rebels, while the confederates were losing filthy rebels. That's the first difference. In both cases the parties entered into rebellion. But the colonists also did not pretend that their actions were permitted under British law. They knew that they were taking a chance with their necks, they knew that they would have to fight for their freedoms, and they didn't complain about it. That's the second difference.