That is, if you go to a doctor's office, they can try to collect payment upfront, but if they send you a random bill after the fact without your explicit price consent, it doesn't have to be paid. Similarly to how I can send a bill to y'all for the privilege of reading my post (and justify by saying it took me years of expensive training to obtain this knowledge), but you shouldn't be required to actually pay me, of course.
Emergency medicine OTOH should be socialized - everybody is covered in the US by Medicare. For every emergency admission facility can charge Medicare for all up to $X (say $300 in Kansas and $500 in San Francisco) and have to make do with that money. Patient gets between 0% and 30% copay depending on whether they are trying to abuse the system or came with a legit reason. This is the same as Kaiser today, but on a National scale.