The reality is that for the majority of physicians and hospitals, there is no way they could survive in refusing Medicare. They would go out of business in short order. Medicaid, maybe, depending on the state. A whole lot of physicians limit the percentage of Medicaid patients they take because the reimbursement can be so much lower than Medicare.
A lot of physicians fantasize about opening a concierge practice, or a cosmetic/wellness/lifestyle practice that is cash only, but unless you practice in a wealthy urban area with lots of well-heeled patients with the discretionary cash to spend, it remains pretty much a fantasy. We all want to be a cosmetic dermatologist in Los Vegas doing nothing but Botox and fillers all day for cash at the time of service and no insurance billing, but there are only so many practices that such an area can support.