Secession would be the wrong answer. If there were a CWII it would be to re-establish the constitution and the republic and to do what should have been done in 1865 — throw out the democrat party, outlaw it and if necessary hang the traitorous leadership of the party. Those who don’t like it can move Canada, Mexico or France where they might feel more comfortable.
I see your point, but look at the numbers. What are you going to do with places like New York? I just don’t see that as realistic. You would be ensuring a war that killed millions. Secession could be peacefully achieved. Over time more states might join the break-aways as their model proved superior.