All those businesses you mention above pay tax. The jobs created attract income tax, the companies pay corporation tax and the services attract VAT.
So why is it so unthinkable that some of this tax goes towards expansion that would lead to more of that income in the future?
Fair point, but the big question is how much? and on which parts of the project?
My two pennies....
Land Purchase - Heathrow should pay
Site development - Again, Heathrow should pay
Transport links (Motorway/Rail), 50/50 between Heathrow and TfL/DfT
Everything else - Probably Heathrow as well, unless i miss something major
But then we're into the charging airlines more, which is also a contentious issue (for another time)...