Why is the government even involved in this decision?

Whether, where and if on the subject of new runway capacity in the SE has been an argument rumbling along for the entire lifetime of our latest intern here at the ASI. It's entirely possible that the shouting match will continue to rumble along until his scheduled retirement date if the past is a useful guide to the future. And Jeremy Warner manages to get close to what we think is the correct answer:

This is simply to approve new airport capacity at both Heathrow and Gatwick, and possibly Stansted as well, and let the markets decide which to back. Whatever the outcome, they are more likely to get it right than the politicians and the civil servants.

The only reason we don't say it is the correct and complete answer is because Warner is betraying his less than total and complete belief in markets. Something which we agree we are rather absolutist about, the joys of markets and their outcomes, but then there's no shame in being absolutist when you are in fact correct.

And the point here is not that markets are just more likely to get something right than politicians and bureaucrats. It is that the market outcome is the correct outcome, by definition. The market simply being a reification of the voluntary interactions of the some 65 million people in the country, said voluntary interactions obviously being all of us having our little vote on the outcome we desire. And thus the outcome from those voluntary interactions is the correct outcome, whatever that result is. If it's no new runways, three or more of them (why not expand Basildon to take 737s and A320s?) or any other possible permutation of the numbers, just letting everyone get on with it is in fact the correct answer as, by definition, that's what will produce the correct result.