“To coerce the states is one of the maddest projects that was ever devised. Can any reasonable man be well disposed toward a government which makes war and carnage the only means of supporting itself, a government that can only exist by the sword?”
Alexander Hamilton, New York Ratifying Convention
Hamilton never said the Union could not be defended or that federal property could be attack or seized. He opposed the NE attempts to secede.
States could not be coerced to join by force. Two stayed out of the new Union for a while and that was legal.
He would have been first in the field to defend the Union.
If secession is legal where does it stop?