I have a lot to say about all this. I live and work in LA, which is home to normal people, as well as some of the most unreasonable, entitled, narcissistic, pseudo-science following, trend-loving and unburdened-by-logic humans that can be imagined.
First off, let me say I hope to never be a part of someone getting seriously ill or worse through anything I prepare, whether it is "my fault" or not. Sort of a hippocratic oath, I suppose. My friend is nut allergic, and one time he showed up at a party where he wasn't originally going to attend. So I made turkey burgers with feta cheese and pine nuts. But surprise, he showed up, and he forgot to ask, and I didn't think about it. So of course he had the turkey burger and had a mild reaction. I felt terrible. Never want to go thru that again.
People have a very complex relationship with food. Many people have no discipline or willpower when it comes to food or certain foods. I have several friends who are lactose intolerant, yet will have ice cream from time to time, without lactaid pills, knowing full well what will happen to them later. People negotiate with themselves, and "treat" themselves to food, even if it has significant negative consequences. Or, "I know I shouldn't, but...." like they're getting away with something.
There are celiacs, there are people with real allergies and sensitivities. Myself, I have always loved mussels, I used to eat them without any issue, but for whatever reason in the last few years, I can't keep them down. If I'm cooking it, I can taste the sauce, but if I eat a mussel, it's bad news. Other mollusks, no issues at all - oysters, clams, limpets, shellfish, other seafood-no problems. So it's possible to have very narrow sensitivities/allergies.
On the other hand, people have learned to say that they are allergic to things because it gets more attention at restaurants (or in our case, catering). But as mentioned above, people often give in with varying proportions of anxiety of symptoms, possible discomfort and distress, fake guilt, real guilt, or no consequences at all.
People are surprised when they go on a voluntary gluten free diet and they lose 30 pounds. Wheat is a good chunk of the Western diet, so removing wheat removes whole categories of food, so of course they lose weight.
An annoying trend is people showing up to weddings or sit-down dinner events without letting their host know about their food requirements, and asking "what are my ______________ options?" Insert gluten-free, garlic & onions free, dairy free, vegan, vegetarian, no-carb, etc.
We did one party for an actor who made a big deal out of food being kosher-style and prepared in his kosher kitchen, and the other food being made out of his non-kosher kitchen. No problem. The servers were briefed that he is to be warned of all appetizers with any dairy, so as not to violate the beef and dairy rule, since he was planning to have steak. He had a fit at one point and demanded we go out and buy and prepare a separate kosher chicken for him. He ate all the appetizers. He ate the cheese course. He ate steak. He didn't touch the chicken. Broke all his own rules. Religion-based rules. Oh, well.
Oh, the rewarding, wonderful, annoying world of food.