Put another way, a mars colony that is not mostly self-sufficient is a death trap, because the lead time on any supply shipments or rescue attempts is monumenta

Put another way, a mars colony that is not mostly self-sufficient is a death trap, because the lead time on any supply shipments or rescue attempts is monumental even if funding is unlimited. There will be ever-present pressure to increase self-sufficiency. If complete self-sufficiency is technologically achieved (and there aren't inherent, unavoidable issues with propagating humans on mars or obtaining resources/energy), earth-based corporations and governments have virtually zero leverage over mars, so independence follows naturally.