Public systems can work very well and I can’t name one system which went downhill very quickly.

Exactly, the NHS is only going downhill because the dominant ideology among MPs has been that the NHS is the first place to get gutted for cheap savings. A lot of very efficient systems were removed and farmed out for "cheaper" private systems, that end up being rather costly in the long term with respect to increased error, price rising, and all the myriad ways incompetence and explicit money-grabbing messes with healthcare. They gutted the administration systems and now doctors have to work overtime on the weekends just to get their notes in the system, and now because doctors are overworked, they're putting more work into the hands of the incredibly underqualified PAs. And on top of all of this, repeated mismanagement of the money that is distributed to the NHS — including, of all things, incredibly inept bartering, putting hospitals on a "target system" where underfunded hospitals are given less money for not hitting targets, etc. It's a complete joke, but every step was damned near deliberate for the case of farming public money into the pockets of the friends of MPs.

The problem with the system in the USA is that paperwork can make all the different in costs. The burden is on the individual to comprehend all the implications of their choices. These choices are beyond do I want my ailments addressed.

Often, people in situations where they require healthcare are least able to assess the implications of their choices, as well. It is very literally praying on the sick.

You could provide every American with extremely robust healthcare for a trillion dollars a year. Probably less as you allocated resources based on need.

We choose to spend that on the military. Basically you can choose guns or butter, we choose guns and empire. Whether that is a “correct” decision is an exercise for the reader.

The US spends more on healthcare than arms.

You could argue for lower defense spending, but there’s a hard lower limit (which is unknown) and if you cross that threshold, the world changes for the worse very quickly.

The rules-based order is underpinned by tanks and planes and nukes. Diplomacy is a layer of abstraction over violence and potential violence.

Medicare costs $800 billion/year and only covers 20% of the population. They are on average the most expensive 20%, but I doubt you’re going to cover all the rest for another $200 billion.

Medicaid is another almost $1 trillion/year.

I've resorted to calling this kind of breathless fearmongering out for what it is. There are too many people suffering too greatly in the existing system to be civil at the expense of maintaining the fictions of libertarian idealogues.

Hyperfixation on an idealistic interpretation of real-world dynamics will always be thought-terminating. In the dichotomy of map vs territory, the map is definitionally a cliche. We can be better than that.