My last set of flights, the very young couple in front of us had an "emotional support dog" that was pretty clearly not a true support dog. They kept passing it around to the people across the aisle, waving it in the air, and basically treating it like any normal pet was. There was even some discussion about how cute the dog was and that their parents had been fighting over who got to keep the dog over the vacation period. When queried the flight attendant said that it was allowed out of the cage, which means they were going with the support animal excuse. My wife and I are both somewhat allergic to dogs, and of course this was one of those types that we tend to find affect us pretty easily, so needless to say by the end of the flight we were both pretty well suffering from our allergies. (Add onto that, asthma and heading to a higher altitude, and that first day of getting acclimatized definitely wasn't particularly pleasant.) I have zero belief that it was anything other than a pet.
Earlier in the day on the bus from parking to the airport, we did also run into a service dog in training. Apparently the dogs first set of flights it was going to be experiencing, and even then, it was better behaved than the dog in the cabin with us. I recognize that there is a need for legit service dogs (and that those dogs need to experience this situation in training). I also recognize that there are people that have legit emotional issues that there are dogs that help with that. I'm not really sure what the best option is to try to respect someone's privacy and yet screen for whether they're abusing the system is, but right now, the bar is too low. (And I'm not overly convinced that these changes Delta is making really moves the bar at all.) I do think banning the exotic animals is an improvement though.