I agree they should be banned totally.
Aeroplane cabins are pretty gross anyway and between flights they don't get much of a clean. What's to stop someone eating a bag of nuts on a flight then touching the seats, dropdown table, toilet door, etc. and then someone with a severe nut allergy getting on the next flight and sitting in that same seat? It's a scary thought!
I suppose you could say the same about any public place but in general I'd assume you'd be less likely to touch something that's been in contact with someone's nutty hands than you would on a flight where they're commonly served!