It's the principle of the thing, everyone is in on it these days with their hands out for additional fees and charges. What next, railway stations charging for dropping off passengers ? The airport gets a passenger service fee from the airlines for every pax that departs from there and screws the retailers who in turn screw the travellers with inflated prices.
I already try and avoid flying long haul out of the UK due to the APD, preferring to make my way somewhere else and leave from there instead. I've arrived in the UK and stopped over in Paris, Zurich and Dublin on the way home and enjoyed visiting a new city with the total cost similar to leaving from LHR, once other countries lower departure taxes are taken into account. Amsterdam is next on the list as a couple of Eurostar tickets and a night in a hotel, or a 24 stopover with KLM can be had from the savings.