I used to work in the ER (and also rotated in the triage) and it was one of the most frustrating jobs that I've ever had. Sometimes I would leave people who came in complaining of chest pains waiting BUT it depended on how the person looked, their history, the description of the chest pain, their age and their ECG. If someone is 21 and has a job lifting boxes and comes in complaining of chest pain, my first thought would be musculoskeletal instead of an MI since that's highly unlikely at that age. That's why you have to do a thorough physical and historical assessment. Is it an actual MI vs an anxiety attack? So what if it's an anxiety attack that's brought on the symptoms of shortness of breath and chest pain and there's someone who is having a dissecting aortic aneurysm? One is actually an emergency while the other one... not so much.
The ER is such a zoo that it's impossible to please everyone and at times you have a lot of people waiting in the front and in the back. The patients in the front have no idea the chaos that is going on in the back. The back is getting killed with patients from EMS (some who don't even need to be there and some who do) and patients from the helicopter that have burns, gunshots, stabbing and have been in mvas. At times there are multiple codes going on, patients bleeding out and other emergency issues and you have someone that's come in with back pain for the last 6 months yelling in your face that they've been waiting a long time.
It's really tough but I understand your anger as well.