Emotional Support Animals have gotten out of control on planes, largely because you can literally search online, submit a paper or two and some bucks, and have an official certification that you are allowed an ESA to travel with you. It's a scam.
All due respect to Maximillian, I know he has a tough line of work and he sees people who could legitimately use an ESA to better their own life, but on planes these days, it largely seems like a scam.
Sat next to a passenger with an ESA dog from DTW-EWR and that dog growled numerous times at my (aisle seat) and the middle seat passenger, and barked at us. I didn't get any feeling that this animal had been trained in any manner to be an ESA. More like the passenger throwing on an ESA costume on the dog and off we go to save a few bucks and travel with the dog on them.