You're tacitly claiming that the claims of the southern states had the same moral status as those of the colonies. There are good arguments to be made to support that position. There are also valid arguments against it.
But we're not talking about the Declaration. We're talking about the Constitution, and whether it gives the Federal Government the right to suppress insurrection. It does.
Not tacitly anymore. Same moral plane. The right to self-government that we revere in the Declaration applies equally to other groups even when we might not agree with their purpose. The colonists were slave holders and slaver traders, so they had no higher moralilty if that is the issue.
But we're not talking about the Declaration. We're talking about the Constitution, and whether it gives the Federal Government the right to suppress insurrection. It does.
No disagreement about putting down an isurrection, but insurrection and secession are different. That said, the Revolution was insurrection, illegal, treason to the Crown, and a great idea.