many providers that won't take Medicare, but plenty that won't take Medicaid. And Medicare typically pays less than most private insurance, which is why folks like your friend justify taking Medicare for their base overhead needs, while supplementing that with the concierge fees in his case, or private insured in other cases for their profits.

Medicare mostly gets away with their lower payouts because there are still plenty of ways for providers to offset them for their desired/needed margins. Once that disappears, I suspect we well have some serious problems most people aren't considering, or just don't want to.

This is why it bugs me a bit when I hear people describe single payer as "Medicare for all". No Medicare gets away with what they do somewhat because it's not for all (and we've allowed it to run in a way that is destined to become insolvent if untouched). Single payer would really be more like Medicaid for all. Or at least all that couldn't afford to pay your friend his concierge fee. Which would have to go up even more if he were getting Medicaid reimbursements.