> do you have some reason to believe the size of pools in a market with less interference would result in unreasonable premiums?
Demonstrably so. Just look at pre-Obamacare "high risk pools" for concrete examples. https://www.kff.org/health-reform/issue-brief/high-risk-pool...
You'll also see it in other insurance markets, like life, house, car, malpractice, etc. - many people are largely uninsurable in these markets.
> What is 'large enough'? The populations of many entire European countries are dwarfed by the number of subscribers to several health insurance companies in the US.
It's not so much raw population as how much you're allowed to slice it up. A decent sized city is big enough - many corporations of a few thousand people self-insure as it's cheaper.
The problem is when you allow insurance to pick their customers. They just pick the healthy ones, if allowed.
> And our health care system requires subscribers to insurance companies to pay those insurance companies to A) provide charity to people who wouldn't be able to afford to buy insurance in real market...
You are using some very weird definitions of "charity".
Obamacare's subsidized premiums aren't shouldered by the insurance companies, they're provided by the government. Those insurance companies are making bank, not providing charity.
Single-payer or income-based subsidized healthcare isn't "charity". Insurance paying out more than premiums taken in for a particular subscriber isn't "charity", it's how insurance works.
> Is it really any surprise that system gets expensive?
Oh, not at all, but that's because we've picked the least cost-effective bits of both private and public healthcare systems to combine into a monstrosity.