I don't think anyone is doubting that there are people who seriously can't come in contact with gluten. I think the people who see the trend happening and assume it's the healthier new diet to have but then complain when it costs extra to have gluten-free items or items that are verified to not be cross-contaminated that we are complaining about.
I have severe, life-threatening allergies and I totally understand that it costs extra to make non-dairy versions of meals, and soy is extra, and that making sure a facility/restaurant/whatever is absolutely not being contaminated costs extra in labor, education, products, etc. Yes, it's not MY fault that I have these allergies, but it's my lot in life and I've accepted that a latte is going to be extra for me. And I'm happy to pay more for a meal at Ethos, where I know I don't have to stress out before taking the first bite, than at a random restaurant where there's always a slight chance I'll end up in the hospital, or worse.
And if you want to talk said kids at birthday parties- I grew up never having a birthday cake, and watching other kids have ice cream and pizza and cake at
my birthdays (because duh you have to feed your friends what they expect when you're a kid) and my mom would either have a bowl of grapes or baby carrots or a Hydrox cookie (the pre-oreo that was naturally vegan) and stick a candle in that for me to blow out on my birthdays. I would just advise instead of getting defensive try to educate us more about the disease.