I never bought that argument. It's like some secularized version of America as a City Upon a Hill. The isolationism works for like 50 years or something, but afterwards the entire system is just going to be integrated, just like any new settlement on Earth was that served as a temporary refuge. Distance that seemed to provide safety is going to go from large to small to non-existent very quickly as technology develops, and probably much faster than in the past.

Any global extinction event is then just going to be a solar-system extinction event, Expanse style. To save enough humans from extinction in case of catastrophy probably some vaults are enough.