- Drug companies that lobby to ban older inhalers whose patents are running out, so they can continue selling new patented ones at high markup.
- Drug companies that lobby Congress to create demand for a product, then jack up prices to $609 per unit to deliver $1 worth of a drug.
- Private insurance companies created as an accident of history, lobbying to perpetuate a system that routinely denies health care to people who most need it. Before the Affordable Care Act, they would deny coverage to people who they knew would be a net loss. Now, they offer poor people plans costing $1,000 per month, where they don't even cover anything under $5,000.
- Health insurers may engage in shady practices. Just one, now deleted comment:
[Insurance company] had my parents sign a bunch of stuff that absolved them from paying for my burn unit bills just days after [I] was burnt. My parents [don't] even remember signing them since they themselves were in shock.
- Insurance bargaining causes providers to keep list prices of 5x what services actually cost. If you lack insurance, you will not only pay out of pocket, you'll pay 5x the price and go bankrupt.
- No dental care for the poor. I estimate at least tens of thousands are left with decaying teeth they can't afford to fix. Most Americans can't afford a $500 surprise bill, and dental care is not covered by the ACA, so they don't have insurance. Tooth infections are left to deteriorate, with chronic pain that lasts for years, until the infection enters the bloodstream and the person visits the ER. Once there, it depends on the provider whether they will do what they can to save the person, or neglect to look at them seriously (so they die) because no one pays for it. Young people (with work, and young children!) have to rely on charity to not die due to their teeth.
There are countries where single-payer systems appear to work, but have complaints. Complaints arise because no such system works by addressing all of their populations' health care needs. The potential cost of that would be infinite. It is in fact not the budget of the system that stretches to cover health care, it's the other way around. A budget is established, which is as much as people are willing to pay; then health care is made to fit within that budget.
When I say health care is "made to fit", I mean people are having to wait for health care in certain cases, and some of them die before they get it, or they can choose to pay for it themselves. This goes especially for the elderly. If you're old and need heart surgery, you get put on a queue that's 18 months long. If you survive by then, you get the surgery. If you do not, that's a saved cost for the system. If the queues are structured sensibly, this does not end up really affecting average life expectancy: people who end up not getting treatment are those who would die soon, anyway. However, it makes it appear as though the system is heartless, because it has to economize, and somehow ration access to health care.
If single-payer care existed in the US, it could not work any differently. Infinite amounts of care cannot be paid. If tax payers are willing to pay $4k per capita, that would be the budget, and the health care would be rationed out. This means not every obese diabetic necessarily gets treatment, and may die.
This differs from private health care, not in that care is not rationed, but that it is rationed so everyone gets something, instead of some people getting nothing, and others getting maximum possible care. Under single-payer, health care access is simply not completely based on the moneybags you have.