Medicare is hugely broken and barely works even for those who are eligible. You still need to get private insurance (called gap insurance) for many, many things.
When I had to switch from BCN to Medicare after I became fully disabled, one of my prescriptions went from $200 a month to $3500, and I started getting denied for routine tests. I was denied a heart cath my cardiologist ordered. I’ve had to stop 4 of my prescriptions because of cost, which of course has made me even more sick.
Even in some utopian daydream, that’s nowhere near ‘universal healthcare’, and expanding that broken system is not a solution.
eta: The US needs actual universal healthcare that’s not inexorably tied to privatisation.