The reason why these systems work well in France (and in other places) is that they are relatively small systems serving a more homogenous group of people (or were until recently). The larger the system gets, the more it breaks down, as is happening in the UK right now.
Also, if you have a lot of immigration that taxes the system (see UK). The more people you have not working and paying into the system, the more fragile it is.
You also need a very high degree of regulation of doctors and other health workers and of hospitals etc. to make a single payer system work. Otherwise you get rampant corruption and fraud (see our Medicare system). The larger the bureaucracy the more waste and fraud you have (see UK see our Medicare system and VA system).
What might work is a State by State system (not Federal) where you have to pay into a State health tax system for 5 years until you are eligible for “free” healthcare.
If we had real insurance, that was ONLY catastrophic insurance, and everyone paid out of pocket for routine health care and meds, then you could also have a robust ‘single payer’ system.
With the system we have now there is so much waste and fraud in the system because of the humongous bureaucracy.
There is not perfect system. The best system (not perfect) would be free market where doctors and hospitals and drug companies have to compete.
What we had before were State sanctioned insurance monopolies and also huge government protected monopolies in Pharma. That was kept in place with Obamacare (and I guess now in the new proposal). This cannot work.
‘Single payer’ could work on a smaller scale ... or with massive amounts of oversight. Think of it this way. Our Defense system is ‘single payer’. And we have large entrenched special interests who lobby government for defense contracts, and a lot of waste and fraud. We could spend probably half what we spend now on defense and still have the strongest most capable military in the world.
The same would be true of a ‘single payer’ medical care system. It would be huge and unwieldy with an ever growing bureaucracy IMO. Otherwise, I have no problem with the concept as long as everyone pitched in. It’s the size and powerful entrenched interests that would be created that I have a problem with. Which we have now but it would be worse.
The VA is single payer, MediCaid is single payer, MediCare is single payer.