I think the main problem with single-payer to a lot of Americans is their lack of understanding of how it would work. Here's a simple plan for consideration:
I'll have to start with a few rough numbers.
Last year, total healthcare expenditures were $2.4 trillion, so I'm going to use $2 trillion as a base to start with, for a couple of reasons: No. 1, there will be savings from going to this route (more than that, I believe); and No. 2, the most recent tax revenue numbers I have are for FY2007. In 2007, total Social Security and MediCare taxes were about $850 billion, of which some small portion were for uses other than healthcare.
The current employer/employee contribution is 6.2% for SS and 1.45% for MediCare. Double that if you're self-employed (I know this well). This tax only taxes the first $106,000 of income (which is all of your income to 90%+ of US wage earners), a fact that is not as widely known as it should be.
My rough numbers indicate that if we eliminated Social Security and MediCare and replaced them with a simple US care plan, we'd have to up the flat-rate payroll taxes to only about 10%, providing we do 3 things: We continue the employer/employee split (open to debate), we tax short-term capital gains as income taxes, and we completely eliminate the cap.
The simplest way to explain this is to say that nearly 1/3 of the earned income in this nation is not currently subjected to FICA because it's beyond the $106,000 cap, and none of the unearned income in this nation requires any Social Security contribution at all.
This would also have the added benefit of freeing pension funds and businesses from the incredible burden of providing this benefit, which increases yearly way beyond inflation.
Of course this would mean that you'd have to pay $10,000,000 if you "earned" $50,000,000, even if you structure the earnings as gains. (Cue the screaming from the right!)
Look, I'm sure this is overly simplified, but we have to start somewhere.