The simple problem is that we already have the long lines and shortages that are being wailed about regarding national healthcare.
It is coming in the form of "we are sorry, we are not taking any new patients right now".
Medicaid is fundamentally flawed in this regard, and while I support the expansion, I think we would be better off phasing out Medicaid and replacing it with a 100% premium support subsidy, and with a public option in the mix among a range of competitors. Try getting that through Congress!
That being said, having the Medicaid expansion does 2 things that are beneficial, because that ER cost is now covered.
1) That cost is not being spread to other patients to cover uncovered treatment.
2) The Hospital won't be forced to close its doors because of uncompensated for care.
Because Hospitals have to take patients regardless of coverage, that means we essentially have universal "sick" care implemented in the dumbest way possible (an unfunded mandate).
It is cheaper overall, and cheaper long term to cover those patients and keep the hospitals open, then it is to let hospitals and doctors go out of business. Seeing as we already have shortages, that would only make it worse.