This is somewhat of a myth; at least it is nuanced. The care in the ER is to stabilize the patient, not fix them. They provide acute care only.
Even acute care can be quite limited. People are triaged based on how acute their case is. Many languish in an uncomfortable waiting room for hours till they crash or leave.
This rationing is done by limiting the beds so that the ER is almost always over capacity. This is by design. Since ER are cost centers, when a hospital asks for a building permit from the municipality, the number of emergency room beds open to the public is the primary negotiation. It's the bottleneck that limits costs.
Emergency beds equipped to handle trauma, e.g, gunshot wounds or car accidents, is even more limited. To avoid costs, many hospitals simply do not have a trauma center, unless the municipality agrees to have significant subsidy. People die in ambulances while they search for a hospital with an open trauma bed.
This is a complex and heartbreaking topic.
Taxing everyone to hell to cover every health expense is immoral.
Universal healthcare is such a moral sham, and what we have now in the US is also pretty bad. There is a better way.
If you're trying to get enough hospitals to do this that people don't just go to a cheaper hospital, then almost all hospitals are going to have to raise their prices... and that's effectively the same as a tax. They're "robbing" every patient the same way.
The hospital can turn of course offer to foot the bill, but can do so only after you’ve exhausted other options. But none of this is forced.
1) More expensive healthcare, to cover for these cases directly in a fund or via third party insurance.
2) Healthcare scarcity.
You can't draw blood from a stone. Healthcare investors/workers at large don't get in to become a charity so your "solution" comes with explicit downsides you should mention.
No solution is perfect, but that’s a world that’s more personal for those helping and being helped. It also is more economically efficient. I’m not saying this is the only solution, but one that starts with robbing your neighbor is the moral low route and we should and can do better.