Righto. So what are "these ends" that morally justify rebellion when the existing Form of Government becomes destructive to them?
The Declaration is essentially a moral document. The Founders could simply have declared their Independence and proclaimed their willingness to fight for it, and let it go at that. But instead they spent considerable time and effort to develop a document that explained why they believed what they were doing was right.
So what were "these ends?"
Why, the rights to "Life, Liberty and the pursuit of Happiness," held by "all men (who) are created equal."
The American Revolution was morally justified only because it was intended to expand human liberty, not just because the Americans were unhappy.
A revolution by group A to impose or increase their dominance over group B is therefore by definition not justified by the principles of the Declaration.
Secession was not done to enhance or expand "Life, Liberty and the pursuit of Happiness." Rather it was explicitly proclaimed by those seceding that they did so to prevent the threat of some of their people gaining those rights.
There is also the little bit about "Governments ...derive ... their just powers from the consent of the governed."
Blacks and slaves in the South were part of the governed. Denying them any human rights at all or possibility of gaining them meant that whatever powers the secessionists might exercise, those powers were not and could not be "just."
The Founders were profoundly knowledgeable about history. They were well aware that many of the revolutions of the past resulted not in an expansion of freedom, but rather in one group (usually the nobility) gaining unjust power over the rest.
They stated very clearly that such a revolt, which was what secession at bottom was, could never be a just one.
You are aware that the guy who wrote that document also owned slaves till his death? (As did Washington.)
Apparently from the example we had from the founders, that morality you mentioned as justification for their breakaway from England, didn't extend to the issue of slavery. Again, *ALL* of the Colonies were slave states when that document was created.
So in the case of American Independence, we still have a bunch of Slave States breaking away from the larger government.
Once again, 1776 was a rather bad example for Lincoln to bring up while commemorating a battle fought to deny independence for others.