It confirmed that secession was not legal. Irrelevant as to when the case came to the SCOTUS.From 1976. Yeah, that isn't even an argument and Federalist 7 says nothing of that sort. It argues why the federal government is needed and the relationship of states to each.
And I meant Federalist 6. Hit the wrong key... though Hamilton's discussion on the topic DOES continue in Federalist 7.