> I'm not sure that's how Medicare is 'predicated' - the fundamental assumption is that you get to a) reduce administrative overhead due to a centralized system, and b) using the power of a single-payer system to negotiate lower fees
This fundamental assumption is wrong, because Medicare doesn't negotiate. Medicare sets rates by fiat, and providers don't have the ability to negotiate rates with Medicare the way they negotiate with private payers. Medicare reimburses rates that are below COGS, which means that providers actually lose money on Medicare patients and have to cover their losses with the margins they make on privately-insured patients. (Medicare acknowledges this, and in fact will pay separate stipends to providers who don't see enough privately-insured patients to cover the losses on Medicare patients).
OP is correct - Medicare's funding model is not sustainable without private insurers to provide the difference.
> it's reducing the profit margin of private insurers, not relying on them to subsidize Medicare
This fundamental assumption is wrong, because Medicare doesn't negotiate. Medicare sets rates by fiat, and providers don't have the ability to negotiate rates with Medicare the way they negotiate with private payers. Medicare reimburses rates that are below COGS, which means that providers actually lose money on Medicare patients and have to cover their losses with the margins they make on privately-insured patients. (Medicare acknowledges this, and in fact will pay separate stipends to providers who don't see enough privately-insured patients to cover the losses on Medicare patients).
OP is correct - Medicare's funding model is not sustainable without private insurers to provide the difference.
> it's reducing the profit margin of private insurers, not relying on them to subsidize Medicare
Uh, where do you think that extra money goes?