Again, I have made clear the problem I have with this situation: if the dog's presence is medically necessary for the dog owner, then the dog owner's presence on the flight (and the dog's resulting presence thereon) is directly threatening the health of the allergy sufferer; however, the allergy sufferer's presence on the flight is not directly threatening the dog owner (indeed, unless the dog owner notices the sniffling, etc, from the allergy sufferer, AND makes the connection that it's the dog that's causing the sniffling, the dog owner would not even be aware of the allergy sufferer's presence on the flight). Therefore, saying that the burden of the inconvenience falls on the one refusing to fly is inherently unfair: the dog owner has no reason to refuse to fly, since the allergy sufferer's presence doesn't affect him - but the allergy sufferer DOES have reason to refuse to fly, and so by default, every time, it's going to be the allergy sufferer who is inconvenienced.