Something nobody else has mentioned her eis that even if a hostpital is required to provide care regardless of your insurance, in practice you're not unlikely to get a lower standard of care if you have no insurance or even if you have insurance that's seen as "inferior" like Medicaid.
Folks without insurance or with "lesser" insurance tende to be poorer. More likely to be seeking pain meds to use recreationally. More likely to be disabled, overweight, etc. More likely to be racially discriminated against or, if white, seen as "white trash". So, having no insurance or inferior insurance itself may get you written off as "probably lying" or otherwise somehow undeserving of the same level of care.
And if that's an issue for life-threatening injuries, it's... probably much more so an issue for more routine kinds of medical care. It's literally not even an option to self pay in some cases. And I don't just mean because it's so expensive. Even if you did say "I don't have insurance, but my bank account has $100 million in it and I can use my debit card," you may be told you're not allowed to self pay.
Poor people without insurance are often sent to alternative care facilities specifically for poor people without insurance. And as you might expect, those places are often very understaffed. So you can expect longer wait times and more rushed care.
Poor people without insurance also often don't get treated early when a problem isn't a huge deal for fear of accruing medical debt. So they're also more likely to end up unexpectedly needing a trip to the ER because that minor infection that, had they gotten it treated a week ago, would have been taken care of with a round of antibiotics has now spread to some much more vital organ.
Folks without insurance or with "lesser" insurance tende to be poorer. More likely to be seeking pain meds to use recreationally.
Do you have a source for this? This sounds wrong, pain pills are rich/middle income people drug as I perceive it. You can't really get hooked up on pills if you never got them by a doctor first.
There are definitely pill mills in the poorer parts of town. And usually poor populations receive Medicaid, which will typically pay for the stuff. Just anecdotal evidence as a pharm tech in a rough part of town during college, but after a while we had to actually stop taking scripts for most pain meds (still got a ton of people using trazadone and stuff, though) because the pharmacist just didn't think it was worth his license if the scripts were tied back to a pill mill.
Adding to this, there is no requirement that hospitals ensure that you are safe when they release you from their care so sometimes people who can't pay for care and have dementia, uncontrolled or poorly controlled mental health issues, or are otherwise vulnerable get left at the nearest bus stop. It even makes the news sometimes because someone got dropped off only wearing a hospital gown at night in winter.
I can't speak for every hospital since I've only worked at a few but this is rare. Some places might still be doing it, dumping people who can't be placed or don't have insurance, but EMTLA was put in place to combat that stuff and the lawsuit and probably fines would make this a bad move. We've kept people where I work for months because we can't place them or psych won't take them. At minimum they're going to a nursing home.
The having money to pay for something and being turned down is such nonsense. I've run into something similar with some procedures I need done. Place would let people without insurance self pay, I have insurance but the wrong kind, they were apparently legally required to bill my insurance but they couldn't. So I was denied service entirely even though I could have paid in full out of pocket. I spent two months getting my insurance to negotiate a contract with them but by then I was/am running into a time constraint and had to switch where I'm going to be an out of state place that can do the same thing but faster. Things are so broken over here.