I think total nut bans in school are wrong for all the many reasons stated above.
It publicises nut allergy as life threatening (which it is) without also recognising the many other life threatening allergies there are (dairy, eggs, shellfish, berries, kiwifruit, etc etc). It can lead to an air of complacency with a reluctance to use epipens, etc, as "DC can't be having a reaction, no nuts allowed".
What would be more beneficial is education regarding allergies in general, an "allergen free" area where susceptible children can eat, with more supervision to make sure that lunches are not shared, with easy access to wipes to keep contamination of hands etc to a minimum and a sink for handwashing before and after meals.
I have anaphylaxis to peanuts and cashew nuts - and avoid all nut containing products as they are often processed in the same plants, leading to potential cross contamination. I don't eat the shared baking at work because I don't want to take the risk. The last anaphylactic reaction I had was from eating chicken at work (from the kitchens, sent up as list overrunning) that I was assured contained no nuts at all. "Just chicken and rice". After I'd collapsed, been resuscitated and sent to ED for observation, someone asked the serving staff whether there were nuts in the chicken after all. "No, no nuts or peanuts at all," was the reply. "Sure?" "Yes, definitely. Oh, well, there is peanut butter in there, does that count?" More education required.