There are very, very few people that my child eating a peanut butter sandwich 20 rows away would hurt. In fact it is questionable if any actually exist at that level.I can understand about the peanuts and peanut dust but not the peanut butter sandwich. And if your child would die if someone 20 rows away would eat a sandwich then others are correct, it is to dangerous to fly or be anywhere in public.
I know of a child, now a young adult that was that allergic. Peanut dust from the front of the plane could kill her in the back of the plane. And it was confirmed by the Jewish Hospital in Denver, the leading hospital in the country in regards to peanut allergies. They said it was the worst case of peanut allergy they had ever seen, and they see most of the worst of the worst.
That said, they managed to fly everywhere. They had their preferred airlines that would accomodate them. But they were reasonable too.
They always called weeks in advance. The plane did not serve peanuts. They had their epi-pens. But it was the dust that could kill their daughter. So, while bags of peanuts could cause her death, sandwiches and granola bars, etc probably wouldn't unless they were in the same row or the ones right in front or right in back.
So, they did make an announcement not to open bags of peanuts. Anything where peanuts were in them, but coated with something to keep the dust down, would not kill her 20 rows away.
They flew on average of 4x per year, many times cross country and with that one accomodation - no bags of peanuts, they never, ever had to use the epi-pens.
This was a little girl who was deemed to have one of the worst peanut allergies in the country. Yet she managed to fly safely with just one very little accomodation. The parents never minded peanut butter sandwiches - unless it was in the row with her. They didn't mind granola bars - unless in the row with her. They didn't mind peanut m&m's as the chocolate kept the dust down and wouldn't hit the air recirculation - unless they were being eaten in the row right in front or right behind her. They never, ever thought to inconvenience a whole plane. They asked for reasonable accomodations. No open bags of peanuts and no peanut products in the aisles directly surrounding them.
FWIW - they were a family of 5, so they would always buy all 6 seats across (in a 3x3 plane) to make sure they weren't asking some stranger to make accomodations.
This daughter just graduated from college and has learned how to manage her allergy herself. She still flies coast to coast and to Europe several times a year without any problems.
Edited to add: The mom also told me that it was the actual opening of the bag of peanuts that would be harmful to her daughter. The force of the opening of the bag released the settled dust into the ventilation system that would then be deadly to her. Peanuts lying around, unless they were being crushed by feet, wouldn't be releasing harmful dust into the air. Anyway, her requests always included the plane not serve peanuts the entire day, so they never had to worry about a previous flight leaving peanuts around. And this from a mother whose daughter would die from the minutest particle of peanut dust in the air.