Their reasons do not matter. They espoused a Natural Law right to leave if they wished, and that is exactly what the colonists did.
Second, yes, if that is true, the South should have let her slaves go, but fought a war to keep them.
In 1776, all the states were slave states. Apparently the founders didn't regard the right to leave as being contingent upon whether or not they owned slaves.
Thomas Jefferson owned 80 slaves when he wrote the declaration of independence.
So the point remains. If the 13 slave owning colonies had a right to leave, why didn't the 11 slave owning states have a right to leave? Why did the Union tolerate five slave owning states continuing to own slaves during the war?
Apparently the Union didn't have a problem with slavery. Again, they had five Union states which continued to own slaves during the war. Apparently the only thing the Union had a problem with was people trying to get away from that North Eastern Power Cabal centered in New York which seems to be more or less the same problem we are facing today.
We are talking about the slaves themselves, who the Southerner's would not allow to leave, but they wanted the same right to do so?
As I said, the American colonists had a right to leave the British empire because they had no representation in Parliament.
The South could not claim this, since they had representation and were in open rebellion.
Slavery was constitutional so it couldn't be eliminated until there was a constitutional amendment, which the North passed, despite the fact that some of their States still had slaves.
They held that the Negro was an inferior being and should be kept in slavery.
So, the real persons who had a right to revolt were the slaves, not the slave owners.