I always go to the man in the street type thing for this. Imagine yourself in the 60s. Now imagine this idea of your time becoming a full blown civil war. You would know, living in that real world, that it couldn't and wouldn't happen. You'd realize such an idea is something for dramatic narratives, like a scifi movie or book, but not real life. America wasn't at that breaking point where someone was gonna secede. We could bloody each other in the streets over demonstrations and counter demonstrations, and you can have domestic terrorism where things are tense, but not civil war where someone secedes or factions vie for power in open warfare.