How many of the States that Seceded, to join the Confederacy, were slave-free States?
The states that invoked the Declaration of Independence in 1861 were like the states that invoked the Declaration of Independence in 1776 - all of them had slaves.
And that raises an important moral question: Can a slave state like - say New York - invoke the Declaration of Independence and seek for itself “full Power to levy War, conclude Peace, contract Alliances, establish Commerce, and to do all other Acts and Things which Independent States may of right do”?
Who cares? The issue of independence does not revolve around the moral approval of others. Given that all the states that became independent in 1776 were slave states, it isn't even a question germane to the topic.
Once again people try to divert attention from the real issue of the war to their pet moral issue. The real issue of the war is that states had a right to independence, even states with morality of which you don't approve.