It's really very simple, and it's contained in the DOI. Which is a moral document. It proclaims who has a right to independence. None of the Founders were so stupid they didn't realize any group with sufficient firepower could obtain their independence by force, so they didn't even discuss that issue. The DOI covered whether they had a right to be free, not whether they had the power to win their freedom.
And that moral right existed when a revolution was for the purpose of securing the inalienable rights of life, liberty and the pursuit of happiness being denied by the existing government.
A revolution for other purposes and in particular for the purpose of denying those rights to others was by the very terms of DOI merely a wicked exercise of physical force.
The men of 1776 did not launch their revolution to protect and extend slavery. In fact, they pretty universally expected the institution to gradually disappear.
The men of 1860 by their own words seceded specifically to protect their institution of slavery. Which means that by the moral principles expressed in DOI it was unjust.
Can’t agree with you. Continuing slavery flew in the face of the Declaration. Fundamentally, both revolutions were against a “foreign” centralized government meddling with the domestic affairs of the aggrieved populations, neither of which viewed slaves as other than chattel. I think the revolution was ultimately to our benefit, but we romanticize it by pretending that the Founders really believed “all men are created equal.” It’s just not true, as evidenced by the fact that the slaves were not emancipated at once. If the principles expressed in the Declaration are the standard by which we deem a revolt justified, then to a certain extent the Declaration condemns the very revolution it announced. No, I see no moral difference. Both the colonies and the south retained slavery for economic reasons.