Willie Walsh opposes unequivocally because the stated all-in cost, even in the best case scenario, is an astronomical £25Bn. And far more likely to be £30Bn+. Senior airline executives tend to have a good grasp of crazy numbers like that. Those figures are all the reason he needs to be 'unequivocal'. And anyone else with an ounce of sense too.
Prophead - you're back to your default position of justifying R3 on operational convenience without regard to cost. IT IS ALL ABOUT COST. Circa £30Bn all-in is too much many times over. Despite wishful thinking, afew extra regional domestic flights don't come close to offsetting that inconvenient reality.
And yes, the core issue is limited runway capacity in the SE specifically. It is not a matter of national benefit, though wasting billions would be a matter of national concern. There is no 'win-win' option if thirty billion is wasted trying to make Heathrow work. But one new runway each for Gatwick and Stansted at a combined lower price just might be. And they're home to the no-frills behemoths - the sector driving the real growth in demand for runway access.