Uh, no. "Medicare pays a fixed amount for your care each month to the companies offering Medicare Advantage Plans." [0] So although the Advantage plans are privately managed, the premiums are subsidized. I don't think this counts as "leaving" Medicare.
[0] https://www.medicare.gov/sign-up-change-plans/medicare-healt...
By that logic, there's no way to leave Medicare, because you can't stop paying taxes for it or "disable" your eligibility for it (and all of the restrictions that Medicare eligibility brings for people on private insurance).
People leave Medicare to the full extent allowed by law. Unless you want to claim that people using school vouchers for private schools is a demonstration of their satisfaction with the public school system in their area, you can't view their use of Medicare Advantage as a demonstration of their satisfaction with Original Medicare either.
It certainly doesn't indicate dissatisfaction with the fact that the money for those vouchers comes out of tax receipts! The primary education system is a single-payer system, and the use of vouchers doesn't change that.
You're basically arguing a tautology: Because there's no legal way to fully opt out of the system if they dislike it, people can't leave it (by your definition), and you're then saying that, because people don't fully leave the system, that means they don't dislike it.
40% of people choose not to use Medicare, to the extent that's legally possible. The program that they choose to use instead outperforms Medicare on every key performance indicator (medical outcomes, cost, patient satisfaction), while also underperforming the same private insurers on those same indicators. It takes some real contortions to look at that data and use it as evidence in favor of a single-payer system, or even evidence that patients like Medicare, but if you're fully committed to interpreting available data in a way that supports that end goal, I guess that's all we can really say.
> The program that they choose to use instead outperforms Medicare on every key performance indicator (medical outcomes, cost, patient satisfaction), while also underperforming the same private insurers on those same indicators.
Cost to whom? I don't see how Medicare Advantage can cost less to patients than Medicare; nor does it seem likely that the premiums for a private plan are less than the subsidized Medicare Advantage premiums. (Re the latter, I guess you didn't see my other reply to you: https://news.ycombinator.com/item?id=16979926)
How do you think Medicare works? Do you think that, once you're covered by Medicare, you just show up at a doctor or hospital, flash your government-issued Medicare card, and receive free treatment for any covered services, without having to pay anything out of pocket?
(For the record, that is not how it works. Medicare is not free for patients. Premiums are neither your only nor your largest expense.)