Money spent inefficiently on healthcare is money not spent on other important problems (e.g., climate change)

This is a misconception that always limits the effectiveness of the government's ability to act as a fiduciary for the citizens. A single-payer healthcare system would be extremely "deflationary", not only costing less but also causing an estimated million workers to be involuntarily unemployed.

Every politician that advocates for such a program immediately follows that advocacy with some plan to "pay for" the benefits via higher taxes or spending cuts in other areas. If implemented, such a plan would be a disaster for our economy, especially if it followed events that already create instability, such as another pandemic.

Just when a million workers would need income support and retraining massive amounts of dollars would be diverted from the private sector to the government in taxes where they would be extinguished by the debt that originally created them. If this unintended consequence happened in today's political environment it would be worsened by the disjointed structure of our unemployment system and left mostly to entities ideologically opposed to supporting workers at the state level.

I am one of the most ardent supporters of single-payer healthcare you will find. But I also know that the mistaken assumptions that now guide our monetary and fiscal policy would bring any such effort to disaster unless programs and funding were pre-allocated to deal with the implications of our economic reality at the federal (currency creation) level.

Few present politicians even remotely understand or would be willing to admit to it out of fear of bucking the gross and corrupt incompetence and econ-illiterate propaganda so prevalent in public opinion. The surest way of creating the failure of a system that already costs far less than that existing is to attempt to "pay for" it with taxation.