Its a good point, but banning it is a minimum safety precaution.
I'll admit, I have an emotional tie to this, one of my good friends has a son with a peanut allergy.
I'll admit that I worry a little bit about him, banning peanuts from his school, to me is a wise thing (though before he got there, it was banned anyway).
If I had a child who was that allergic, I wouldn't make his life someone else's responsibility. You just can't expect that no one in the school will ever bring peanut anything. Even if the principal sends Patty-the-PBJ-bringer home immediately, what did she touch before she left? If you read labels, peanuts are EVERYWHERE.
I don't like them, never have, the stench of an open jar of peanut butter used to drive me from a room, but I'm not allergic. I never thought George Washington Carver did us any favors proving they were edible.