So they have to work for the government or they don't practice medicine. That's not going to happen; you're not going to outlaw private practice.

No, they don't.

If you accept Medicare, you're not "working for the government" - any more than defense contractor firms or their employees are "working for the government" because the government is the one paying for their services. Or any more than if you accept private insurance, you're not working for the insurance company.

There is a fundamental difference between the NHS model (like in Britain) or the VA model where the doctors are, in fact, working for the government, and one where the government is the ultimate payor of medical insurance claims but the doctors are still working for themselves or private institutions.

But they will have to accept whatever the government rate is for reimbursement of any given medical service, because the government is writing the checks. And since they're the only one writing the checks (for the most part), they get to set the price.