Not only is lying about food allergies a pain for the chef and cooks, but it creates a sense of "illegitimate allergies". For example, people with Celiac Disease, or other gluten intolerant conditions often get eye rolls when they say they are allergic to gluten.
There's also a huge scene here with naturopaths dealing with people and giving them laundry lists of "allergies". I got a card from a customer with, not a word of a lie, TWENTY FOUR "allergies". Whether they were legit or not, i don't know but some where really really out there. However, even though it meant making 90% of that dish she ordered from scratch right there on the fly, we accommodated because it's what we are taught to do even if it is indeed very out there. Especially at my restaurant which is known in these parts for being very allergy and celiac friendly.