This is exactly it -- in the moment, how is the average person supposed to know what will or won't be classified as an emergency by some insurance provider after the fact? And are you sure enough about it to risk your life on it?
I took my son to the ER recently for an asthma attack. He seemed relatively fine by that evening, but they decided to admit him to the hospital for observation. Unfortunately, the only place with enough nursing staff to administer the medicine every 2 hours was the pediatric ICU. He seemed fine to me--too sick to go to school, but eating and sleeping and playing and generally looking fine--but, hey, I'm not a doctor. We ended up in the ICU and then the general pediatric ward for 4 days for a grand total of about $45K.
Later, we got a letter from our insurance company saying they had reviewed the bill and deemed it medically necessary. Well, good, I guess. But what if they had NOT deemed it medically necessary? Or had only deemed part of the stay medically necessary? How could I have known that ahead of time? I didn't exactly want to check my son out of the ICU against medical advice on the "eh, he looks fine" theory.
The more I interact with the US healthcare system, the angrier I get. It's inhumane. It gets everyone and their weakest moment, and it's hardest on the most vulnerable people. It violates the Hippocratic oath to "do no harm."