There was precious little “peaceful” in the way the slavocracy attempted to exit the union. If one chooses to “exercise their revolutionary right to overthrow” one should expect others to resist it.
First the right of secession had been commonly understood since the ratification of the Constitution.
Second the Confederacy had warned Lincoln not to resupply Fort Sumter. Any nation would consider the occupation of a foreign fort on their territory especially one located in a vital sea port to be an act of aggression.
If you believe as did most statesmen of the US up until at least the 1830s that the member states of the union were sovereign states and that those states had the right to secede from the union.
If the Confederate States had the right to secede then you must conclude that the Confederate States were a sovereign nation after having voted to secede.
If the Confederate States were a sovereign nation then the attack on Fort Sumter was a defensive act.
Even post-Civil War I still contend that any state can vote to secede from the United States. There is no provision in the Constitution stating otherwise.