Why would anyone get upset with soeone else eating? Did they ever consider that they might need to eat? A ban on eating would mean that someone with diabetes could very well be in a dangrous consition by the time they were ble to get off of the train and be unable to take care of themselves.
So bring a granola bar, bag of peanuts, or something else not likely to make a mess on other people's clothing if it spills.
Because some people chew with their mouth open or have other disgusting eating habits. If the train stops short, someones food may end up on someone else's shirt or all over the floor or seat, where it is left for the next person to sit or stand in. What smells good to some people nauseates other people. People who eat on subways tend to be pigs who leave their garbage behind. They also tend to be really fat, which makes sense given their inability to control when and where they eat.
BTW, I am a diabetic and I have never had to eat a bowl of spaghetti, a meatball hero, three slices of pizza, or a KFC extra crispy dinner, while on the subway, to control my blood sugar. I do carry a granola bar, glucose tablet, or small juice box in case I find myself in a difficult situation, but I have never had to pig out on the subway because of low blood sugar.
A diabetic can eat an apple or a candy bar to take care of things until they get home.
A bowl of pasta? No way.