No Founder -- none -- ever claimed an unrestricted "right of secession" at pleasure.
All considered as legitimate disunion by mutual consent, or from necessity caused by oppression.
But secession "at pleasure" was simply treason, for which they had no tolerance.
One might put forth the proposition that the Southern Slave Powers chose the perpetuity of their peculiar institution over the perpetuity of the United States.
No Founder -- none -- ever claimed an unrestricted "right of secession" at pleasure.
That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness.
Meaning, in simple terms, "At Pleasure."