> Notice how no one really lists contingencies for "what if the EU goes off the rails"? There's always an implicit assumption that EU politics will always be "sane" (read: "aligned with my personal politics").

I think it's much less an expectation of sanity and more that the EU doesn't really host or do much of anything actually "important". The USA quite literally runs half the world so people are rightfully worried about it going "rogue".