Why do you keep talking about "pay for that proposal"? I keep saying, we are paying more than enough to cover a single payer system now. ANY reduction from the cost of the current system is a gain.

Because the government has to pay for it. Even if the new system pays the same or less in aggregate, you still have to find the revenue sources for the government to pay for it. We're changing who pays from a mix of public and private to almost entirely the government. We change who pays and at what rates. Which means that the government has to get enough money to pay for all that. It has to be paid for, which presents difficulties.

Most simply, health care consumption goes up. All the uninsured and underinsured people start consuming more health care. Yes, they currently get some treatment from unpaid visits to the ER or out of pocket or GoFundMe - but once they have insurance, they will consume more health care. We have to now pay for all that.

Second, we lose the (mostly) tri-partite rate reimbursement system we have now. Medicare, Medicaid, and private insurance pay very different reimbursement - and Medicaid is especially discounted. Once everyone gets paid the same rate, you lose the Medicaid discount. You might be able to cut the private rates down towards Medicare rates to compensate, but then we start to get into the problem of seriously disrupting provider financial stability. And that's even before we get into the issue of how we're going to set coverage levels so that people with better-than-average coverage don't end up with worse coverage in the new plan.

Third, government's tools for raising the money can't duplicate who's paying today, exactly. Government can impose a payroll tax (which taxes work, obviously), or a VAT (which taxes consumption), or some combination of both - but those won't map onto everyone's current levels of contributions. Lots of people will end up paying less than they pay now. Which means, other things being equal, that lots of people will end up paying more than they pay now. Which is political poison.

So to make this work - to actually pay for it - we need a lot of cost savings to cover: i) the cost of increased health care consumption; ii) the loss of the Medicaid discount; and iii) the fact that the government can't raise enough taxes to match current expenditures without dramatically increasing the total cost burden of the people being taxed from current levels. The savings is what makes it possible.

But it's not enough to cover the increases in costs due to new consumption and the raising of Medicaid (and possibly Medicare) rates. Which makes it all-but-impossible for the government to find enough money to pay for this in a politically feasible way.