I've posted before that I have traveled the world with my show dogs both under the plane and in carriers under the seat.
I met my first emotional support dog a few years ago. One was a yellow lab owned by someone who had lost their parents in a horrible accident and this dog just kept her together. Another was an Irish Setter owned by a Lyme's patient. This dog could sense when the owner was weak in the knees and would prop itself against the person so they wouldn't fall. If I didn't see it with my own eyes, I wouldn't have believed the type of support that they give. It is truly amazing and a blessing. Another friend has a Newfie as an emotional support animal. I'm not sure how an airline would handle that. Other than the drool, the dog is one big moosh.
With that in mind, there are many pax who see an animal and immediately go into a hissy fit. I have paid the insane fees to fly my show dogs. After traveling using a sherpa bag for years, I had to switch to a Tutto Pet On Wheels because it looks just like carry on luggage. Since switching to the Tutto, there hasn't been ONE complaint or comment from anyone about a dog in the cabin. My dogs sleep the entire way and don't say boo. With the Tutto, you can't even see them turn around as you can with a sherpa bag.
I gave up my FC seat assignment last month on a DFW-LGA flight to a man with a dog in a sherpa because he was assigned the bulkhead seat. No one would switch with him, so I did since no one else cared to be "nice".
And for the uninformed, there are over 1500 dog shows in the US every year. With the exception of the week before Christmas, there's a dog show somewhere in the US. And for those of us who have small enough dogs to fit in the cabin is because of the abuse and trouble that the baggage handlers can inflict on some very well behaved, innocent dog. It has gotten to the point where, if the dog has to travel under the plane, that we do everything but put a padlock on the crate so the door can't open. The stories are common and uncalled for.
I have great respect for people with allergies. They should know ahead of time that airlines allow two dogs per cabin as a general rule and should be prepared. And, yes, I'd rather sit next next to an animal rather than a screaming kid with a filled diaper and an uncaring parent or the liquored up pax who smells of scotch or the guy who spits his chaw into an empty glass or soda can and then leaves it in the seatback.
Just a counterpoint and a little extra information for the uninformed. Emotional Support Animals DO exist and they serve a purpose.