I do think that most people, especially families with young children would accommodate an allergy request, but the one time I have taken issue and asked someone (very politely) to refrain fron eating nuts, it turned into a confrontation.
My son and I were sharing an airplane row with a man who had brought a bag of nuts on with him. I had already informed the airline of the allergy and they were kind enough to serve a nut free snack and make an announcement to ask that passengers refrain from eating nuts as the allergy is anaphylactic. After the announcement, he snickered and turned to his traveling buddies behind us and made a rude comment about how he didn't care and he was going to eat his snack anyway. Luckily for me, the flight attendant was awesome and totally advocated for my son and although he put up a fuss, it didn't get too out of hand.
After that, I have been timid about asking people to accommodate us and we do what is necessary to protect our son...even if it means skipping a ride or two. Having said that-We have had APs and visited the parks for years and have never one time had an issue after riding rides. I always remind my son not to touch his face, wash his hands etc...and we have always been fine