The Declaration of Independence did not meet with universal approval in the colonies. And I'm certain the British parliament did not consider it to be a legal document. There is always risk in politics.
The prospect of a packed SCOTUS etc. leaves me to believe a COS might eventually be the only way to avoid violent upheaval. That is the basis of my opinion.
I would agree that it should only be used as a last resort to prevent violent upheaval. This is why I also say the first order of business is to recognize the dissolution of the union ... That way, any state that does not accept the outcome can go their own way in peace.