There always are patients, who could be kept alive at high costs but without much, if any, prospect of recovering.
True... though I'm lost as to how you think that is somehow ethical.
Then explain to me how it is that everyone over the age of 65 isn't immediately put to death the first time they catch a cold by the government since people on medicare (everyone over 65 in the US) ARE on a single payer system.
First of all, I did not say, the government will condemn everyone to death — whether or not they have a prospect of recovering. What I said was, the decision — whatever it is — will be the government's.
Second, I don't doubt, that people with a good chance of recovering will be paid for (except, perhaps, in certain very special circumstance). A cold — or even an influenza — are quite recoverable and the sole payer will pay for it.
Lastly, the Medicare today is sustained not by the beneficiaries, but by the younger people, who pay into it, but aren't yet eligible to use it. Once we have, what Illiberals affectionately call "Medicare for All", belts will have to be tightened — severely...
Apparently you've forgotten that people vote
I'd much rather be able to switch a doctor/insurer/hospital as easily as I can already switch a mechanic, car insurance, or an ISP — from one competitor to another without waiting for the majority of the voters to agree with me. It is just (much) better that way as it is quicker and allows people that wonderful thing called choice.