But we're better off encouraging a single major airport (especially if it's conveniently connected to high-speed rail for Vancouver-Portland travelers). Consider Heathrow and this letter from the Economist:
SIR – The Economist noted that since 1990 the route network at Heathrow has decreased, while transfer traffic has increased (“The right side of the argument”, November 8th). However, the subsequent claim that transfer passengers are of limited economic value is incorrect. It is in fact evidence of the market forces caused by a capacity-constrained airport.
Slots at Heathrow trade for up to £25m ($37m), clear evidence that given new capacity, the network would grow. Until Heathrow is permitted additional capacity, airlines will understandably make the rational, economic decision to focus the limited slots available to them on the most profitable routes. This is tenable in the short term, but over the long term Britain’s economy will suffer from not being able to offer direct links to cities in the growing economies of India and China. Around two-thirds of routes at Heathrow are supported by transfer passengers who make up 25-40% of the people who fly on them. Without these passengers, major business destinations such as Bangalore, Chennai and Seattle would all disappear.
It is naive to think transfer passengers do not offer any wider economic benefits—the direct, global links that these passengers support are Britain’s gateway to the world economy. Heathrow is Britain’s only hub airport and a vital economic asset. If Heathrow is to stay in the global league, then a third runway is vital to keep it, and by extension Britain, competitive.