Why spy? That’s the several-million pound question, in the wake of the Snowden revelations. Why would the US continue to wiretap its entire population, given that the only “terrorism” they caught with it was a single attempt to send a small amount of money to Al Shabab?

One obvious answer is: because they can. Spying is cheap, and cheaper every day. Many people have compared NSA/GCHQ mass spying to the surveillance programme of East Germany’s notorious Stasi, but the differences between the NSA and the Stasi are more interesting than the similarities.

The most important difference is size. The Stasi employed one snitch for every 50 or 60 people it watched. We can’t be sure of the size of the entire Five Eyes global surveillance workforce, but there are only about 1.4 million Americans with Top Secret clearance, and many of them don’t work at or for the NSA, which means that the number is smaller than that (the other Five Eyes states have much smaller workforces than the US). This million-ish person workforce keeps six or seven billion people under surveillance – a ratio approaching 1:10,000. What’s more, the US has only (“only”!) quadrupled its surveillance budget since the end of the Cold War: tooling up to give the spies their toys wasn’t all that expensive, compared to the number of lives that gear lets them pry into.

IT has been responsible for a 2-3 order of magnitude productivity gain in surveillance efficiency. The Stasi used an army to surveil a nation; the NSA uses a battalion to surveil a planet.

Spying, especially domestic spying, is an aspect of what the Santa Fe Institute economist Samuel Bowles calls guard labour: work that is done to stabilise property relationships, especially the property belonging to the rich.

The amount a state needs to expend on guard labour is a function of how much legitimacy the state holds in its population’s reckoning. A state whose population mainly views the system as fair needs to do less coercion to attain stability. People who believe that they are well-served by the status quo will not work to upset it. States whose populations view the system as illegitimate need to spend more on guard labour.

It’s easy to see this at work: Bahrain, Saudi Arabia, China and North Korea spend disproportionate sums on guard labour. Highly redistributive Nordic states with strong labour laws, steeply progressive taxation and tenant protection spend less on guard labour. They attain social stability through the carrot of social programmes, not the stick of guard labour.

In Capital in the 21st Century, Thomas Piketty uses the wealth disparity on the eve of the French Revolution as a touchstone for the moment at which the perception of the state’s illegitimacy goes to infinity, when even emptying the treasury for guard labour will not keep the guillotine at bay. Piketty is trying to convince global elites (or at least the policymakers beholden to them) that it’s cheaper to submit to a redistributive 1% annual global wealth tax than it is to buy the guards to sustain our present wealth disparity.

There’s an implied max/min problem here: the intersection of a curve representing the amount of wealth you need to spend on guards to maintain stability in the presence of a widening rich/poor gap and the amount you can save on guards by creating social mobility through education, health, and social welfare is the point at which you should stop paying for cops and start paying for hospitals and schools.

This implies that productivity gains in guard labour will make wider wealth gaps sustainable. When coercion gets cheaper, the point at which it makes “economic sense” to allow social mobility moves further along the curve. The evidence for this is in the thing mass surveillance does best, which is not catching terrorists, but disrupting legitimate political opposition, from Occupy to the RCMP’s classification of “anti-petroleum” activists as a threat to national security.

Technology also brings productivity gains to social programmes. Basic sanitation, green revolution crops, cheap material production, and access to vaccines and mobile internet devices allow states to lift the desperately poor into a more sustainable existence for less than ever, affording stability to wealth gaps that might have invoked the guillotine in previous centuries. The mobile phone is important to this story, since it’s both a means of raising quality of life – through access to information and markets – and keeping its users under close, cheap surveillance.

The neoliberal answer to this is: so what? If the rich can be richer than ever without the poor having to starve, doesn’t that mean that the system is working? Boris Johnson’s big cornflakes have been sorted to the top of the packet, and have produced so much efficiency that everyone is better off for it, just as market theory predicts.

Even if you think that hereditary dynasties and extreme wealth for the few and hereditary, extreme poverty for the many is morally fine, the reality is that extreme wealth concentration distorts policy. We want policy to reflect the best available evidence, but when legislators are drawn from, and beholden to, a tiny ruling elite, they can only make evidence-based policy to the extent that the evidence doesn’t inconvenience rich people.

It’s obvious that excluding 52% of the population from public life is bad for the economy in Saudi Arabia. It’s obvious that Canada, a country characterised by huge wilderness and resource-extraction, is in terrible danger from climate change and that it’s madness for its oil-backed Tory government to dismantle its world-class climate and environment science infrastructure, literally setting fire to the archives.

It’s obvious that the finance sector is corrupt to the highest levels, and that the City is the heart of a vast criminal enterprise. It’s obvious that homeopathy is bunk, even if Prince Charles likes it.

And so on. A state that is beholden to a small number of people is also beholden to that elite’s sacred cows. It is incompatible with evidence-based policy.

Why spy? Because it’s cheaper than playing fair. Our networks have given the edge to the elites, and unless we seize the means of information, we are headed for a long age of IT-powered feudalism, where property is the exclusive domain of the super-rich, where your surveillance-supercharged Internet of Things treats you as a tenant-farmer of your life, subject to a licence agreement instead of a constitution.