Some of the comments early on in this thread are incredible.
Firstly, there is no such thing as a 'slight' allergy. If there are specific IgE antibodies in your blood, you are allergic to that substance. The level of that does not necessarily correlate to the extent of any reaction. And as for those equating nut allergies to other allergies such as milk, it is generally known that most children with milk or other food allergies, tend to grow out of them. That is not the case with nut allergies. My daughter was diagnosed as being allergic to milk, strawberries and nuts when she was 3. She has had two anaphylactic reactions relating to nuts. Her reactions to milk and strawberries were quite different, and by 7 she had grown out of them and her IgE levels had dropped. Her nut specific IgEs remain high however, and she carries an epipen everywhere. There are no guarantees that an Epipen will be effective, so it is important that there is recourse to immediate medical care. That is not possible at 35,000 ft ! A lot of people think if it doesn't affect them or their loved ones, then it shouldn't affect their freedom to eat what they wish.