I will admit to feeling a slight irritation at all those telephoto lenses, especially when I trip over the chocks or something during pre-flight. But individually they seem to be perfectly nice people.
That's the problem I think. IO540's idea would fall at the hurdle of indvading their privacy or something. After all, they are just harmless people admiring the work of others who they look up to (not sure about that bit). IO540's plan would be seen as personally malicious, wheras their constant clicking away is seen as impersonal (photographing a plane, not the owner) and therefore innocent.
We're stuck with it. What we need to do is get airfield owners to charge a modest amount (£5/day say) for a permit and put the result toward lowering our landing fees. Good business for the cafe, keeps the spotters under control in a compound, subsidises flying which means more aircraft to spot. It works on the railway so why not here?