Suppose Heathrow didn't exist, try writing a proposal for it as we stand today. There is no way it would ever happen.
I'm afraid that is a side argument. You could also say "suppose smoking / alcohol didn't exist, we wouldn't have them today".
Obviously, it would either be an urban area, or green belt!
Exactly. Just where exactly is the perfect place to build an airport? In my experience I'll suggest that some of the world's larger airports (by area) had
near perfect sites - endless prairie for DEN, or better still, barren desert for the likes of DMM or RUH.
Now as
almost all the land in the SE is either already built on, or is
fiercely protected greenbelt, so the easiest option is to expand sites that have already been used as airports.
You could make a similar claim for what might we do if
no airports existed, that the plane was invented tomorrow, and that we needed
just one hub airport for all flights.
That is the
only scenario I could paint for which the 2003 Rugby Airport proposal might have had
some merit, but I suggest that even if we were in that situation, the "single" airport would still end up being much closer to London, because the UK's centre of
economic gravity is still somewhere around Milton Keynes, not further north.
So actually, given the "one airport for London" with none others existing, I'm still not sure we'd be using the Thames Estuary, because it is too far east, and because it would be so much hassle to connect it to the road and rail networks.
But at least if this was the challenge, Fantasy Island wouldn't have to worry about what to do with LHR, as it wouldn't exist!