Secession means armed revolution against the federal government. It means canyons filled with corpses and large parts of the nation turning into Syria or Somalia. I just can’t see it happening in this day and age, the average person is living well on some kind of federal subsidy, they aren’t going to cut off their own paycheck.
Bullsquish.
Secession is a purely political decision to leave a union of states. There's nothing inherently violent about it, unless one side decides to use military force and murder to force the other side to bend to its will.
THAT is the thing that is unthinkable in this day and age - not secession itself. This isn't 1861. Secession by one or more states will not result in the use of force by the U.S. to compel those states to remain in the union. The political and societal will to use brute force against a peaceful political process does not exist in our time.