Pissed at people who fake allergies

I follow another subreddit called onionhate because I'm allergic to onions. I don't know why so many people give the advice just to 'fake an allergy' at restaurants. Maybe I shouldn't be pissed but I am. Maybe it helps since then restaurants get used to the idea of an onion allergy.

What do you guys think of 'faking an allergy' at restaurants when you don't like the food?