I agree that it’s absolutely not okay to bring your regular old, no matter how beloved, PET into a public place as any kind of service or therapeutic dog. It’s not fair to the others, the poor animal who is not conditioned for such a circumstance as flying, and to the system in general.
The fact is, dogs and some other animals have had remarkable therapeutic benefits for a wide range of disorders that are not necessarily immediately recognizable by others - autism, PTSD, diabetes, epilepsy, anxiety etc.
A working dog is either a certified service dog who is allowed in all public places. An emotional support animal is allowed in housing and and transportation.
The point is, a dog doesn’t NECESSARILY have to look like a typical service dog. A person doesn’t always look like they need one. But, perhaps that means that it’s working.
FINALLY, service dogs can be yorkies or even a freaking teacup poodle if it is trained to perform a service that benefits a person’s condition.