With all this talk about families travelling, why do people think that they have a right to fly (out of LHR) on holiday ?

Just like everything else in this society, everyone has a choice. If you feel it's become too expensive (due to BAA charges, APD, fuel surcharges etc) then fly out of another airport, take the ferry/train/etc, go or holiday in the UK instead or simply stay at home.

BAA's main aim is (as it should be) to maximise its profits. Less people flying also means a more pleasant experience for the the rest (leaving aside issues about the environment).