Keep in mind that I'm saying this as someone who decided not to have kids, but...no, I don't think you have a crappy attitude or a reason to feel guilty
at all.
If a child's allergies are so severe that others must be presented with a shopping list, then that child's parents should be the ones to provide the food. Let other parents contribute financially if that's an issue, but otherwise, it's incumbent upon those parents to prepare special foods.
I'm actually a bit annoyed on your behalf at parents who are so cautious that they issue shopping lists telling other parents what to buy and where, but are totally okay with the possibility that the food could be prepared by people who really don't know how to "allergy-proof" their kitchens appropriately to deal with someone with severe allergies.
I don't know about you, but my home contains a TON of allergens and food-sensitivity triggers--peanut butter, strawberries, flour, citrus fruits, you name it. Although my kitchen is clean, I couldn't
guarantee that my husband hadn't just made a peanut butter sandwich on the counter on which I'd be slicing cookie dough.
I wouldn't feel comfortable providing food for kids with life-threatening allergies, and I would tell the parents so. To me, their attitude stinks and sounds more like controlling behavior than genuine concern: "I'll give you a shopping list and tell you what you can prepare, but I'm A-OK with letting it be prepared in uncertain conditions because it's more important for me to be an interfering, dictatorial busybody than to ensure my kid's safety."
A pox on these parents who believe that looking concerned is more important than actually being concerned. I'd suspect
Munchausen by proxy of at least a few of their ilk.