Don't quote me, but I've read many places in the US that ER's are required to take you if you are in a life threatening situation and if you cannot pay, the hospital just ends up owning the costs and then passes those costs to everyone else through insurance fees.
I've witnessed this first hand. For a nonemergency even. A friend with bad English went to the ER to have a rash looked at (not understanding what the more appropriate action would have been).
The ER don't doctor spent about 2 minutes with her and wrote a prescription for some topical thing.
Later the hospital sent her a bill for about $1500. I went with her to the hospital's billing Dept, helped her fill out a form that basically said "I have no insurance and no money".
Legally the ER can't turn you away if you can't pay, in the US.
What they can do - specifically relevant if you're a US citizen - is send you a bill and then after you don't pay it send it off to collection agencies, which then harms your credit rating for the next five or seven years (I believe various states have different laws on when these have to drop off your credit rating, it's usually either seven years or slightly less). This has improved a bit lately, with new credit scoring updates that considerably reduce the hit from medical bill collections on your credit. However it's obviously still a ridiculous situation.
Most non-private hospitals in the US have low income programs you can sign up for (eg if you go into the ER due to an emergency and run up a big bill), that eliminate most or all of your bills if you fall under a certain income level. That's subsidized by government funding programs. Typically though if you're at that low of an income level, you should just sign up for Medicaid anyway. Those programs are usually most valuable when someone in the eg 22-50% income bracket (the most vulnerable in the US insurance system, where you're above Medicaid and below typical good paying career or job status) is caught inbetween insurance / jobs for a number of months and gets hammered by an ER visit.
