I think airlines (as well as their customers) are being unreasonable. LHR must be constrained, and expansion forced onto other airports. What's the cost of a 3rd LHR runway? Bet this money would go very far towards building a Skytrain and new terminal at LTN, a fast rail connection to Manston and/or a second runway at LGW.
OTOH, the suggestion that transit pax don't help the economy of a country is beyond bizarre. Don't these people pay for their air tickets, baggage handling, use of immigration facilities and therefore help keep locals employed? I suppose such a deep level of understanding is not required to run an airline...