Robert E. Lee said that the talk of Sucession was nothing more or less than rebellion.
If Sucession was legal, then the writ of Secession by a state could have been considered by the Legislature or by the Supreme Court. Rather than accept that, the South stole Federal Property, and raised armies, the act of a violent rebellion.
Only much later, after the violent rebellion miserably failed, (in part due to the bravery of entire regiments of southern men who fought against the rebels) was the legal argument raised.
Wrong. The legal argument was raised by Senator John Calhoun of South Carolina in the 1830’s!