Actually, 11 years ago the DOI was debated by American and British lawyers.
The Brit's argued the DoI was not only illegal but was a treasonous act. Because citizens, neither in 1776 or today, have no legal right to establish new laws just because they want to.
The American side's argument was that natural law insures governance can only occur by the consent of the people. And in the face of tyranny are no longer obligated to give their allegiance.
In that debate the American perspective won.
Secession: The Contradicting Provisions of the United Nations