The last time I was in the ER there were a lot of morons there with ailments that should have been treated in a doctor’s office. My rule of thumb is very simple: If it ain’t bleeding, broke, or on the outside when it should be on the inside, then don’t go to the ER.
How about appendicitis? How about a heart attack? How about a deep vein thrombosis? How about pneumonia? You don't want those in an emergency room?
Where did you get your medical degree?
I would be cautious about limiting your judgment to externally visible issues. Last year I was admitted through the ER for elevated ketones (I am diabetic). The discovery of the ketones came later in the evening on a Friday night. On my doctor's advice (via telephone), I went to the ER and subsequently spent the weekend in a hospital bed.
Ketones are not visible, but ketoacidosis can kill you - in a hurry.