My aunt flies frequently for business (at least once a week). She has routinely had to move because of people with pets (or "emotional support animals"). This isn't to be rude, but because she is highly allergic and it is not only uncomfortable for her, but dangerous.

Have you ever been on a flight where someone with peanut allergies is on the plane? The flight attendants announce that someone on the plane is allergic, so peanuts will not be served on the plane as a matter of safety.

The same courtesy should exist for people with allergies to pets. Many of them have to spend the whole flight concerned that they might have a reaction because they are forced to share the same re-circulated air as a pet that is potentially dangerous to them.