"You can't have 100 percent security and also then have 100 percent privacy and zero inconvenience." This is the defence offered by United States President Barack Obama for the National Security Agency's (NSA) massive PRISM surveillance programme, which involves the routine collection and analysis of "metadata" from a wide range of internet and communications networks across the globe. This explanation was coupled with the assurance that, 'nobody is listening to your telephone calls'.

Polls in the United States suggest that the general population is satisfied with this explanation, and with the exchange of privacy for personal security. In the New York Times, columnists Thomas Friedman and Bill Keller have echoed this attitude, offering what they call "balanced" responses to the situation. Much of the critical reaction to the issue, Keller suggests, has amounted to "overblown rhetoric." What must be recognised, he continues, is that a "well-regulated program" will set clear and definite limits that will prevent the system from being abused. For Friedman, the real danger to privacy is not the NSA's PRISM programme, but the consequences of another successful 9/11-like terrorist attack on American soil. If such an event were to occur, he worries, the public response would be: "Do whatever you need to do, privacy be damned." In other words, PRISM is the lesser of two evils.

These reflections do dampen any overly-romantic evocations over the sanctity of "privacy" - however, we have seen this rhetoric before. In his 2003 Gifford Lectures, Michael Ignatieff offered a defence of the "war against terrorism." He began by invoking ancient Rome's willingness to sacrifice all of its other laws in order to defend the security of its citizens: "For what laws would survive if Rome itself perished?" Ignatieff then suggests that such is the choice facing governments when confronted by terrorism. In an emergency situation, "we have no choice but to trust our leaders to act quickly." This includes accepting that "necessity may require us to take actions in defence of democracy which will stray from democracy's own foundational commitments to dignity." In other words, let's not get overly sentimental about moral considerations when faced with a threat to our security - the ends justify the means.

Ignatieff acknowledges that there are inherent dangers in this position (which he calls the "lesser evil"), but argues that these can be controlled by the systems of liberal democracy. We can trust our governments, he says, because they are elected, and are thus kept in check by the need to continually subject themselves to the will of the electorate.

This position is essentially the same one that President Obama employs in defence of the PRISM programme. What is noteworthy, therefore, is to recall that Ignatieff later changed his mind about his argument, and concluded that the war in Iraq had in fact been a mistake. In his article "Getting Iraq Wrong," Ignatieff laments that what had appeared to make sense in theory, did not work in the messiness of reality. Politicians, he observes, do not simply make decisions by soberly balancing difficult options; they are driven by certain interests, including staying in power, but also by personal fears and biases:

"I should have known that emotions in politics, as in life, tend to be self-justifying and in matters of ultimate political judgment, nothing, not even your own feelings, should be held immune from the burden of justification through cross-examination and argument."

What, then, of Ignatieff's previous confidence in the capacity of government officials to responsibly negotiate the dangers of the "lesser evil"? This problem is inherent to President Obama's defence of the PRISM programme. When he states that he "welcomes the debate" over the "trade-off" of privacy in exchange for security, what he does not mention is that this debate cannot really happen, since the details of the programme are to remain secret, "for reasons of national security."

His ongoing aggressive persecution of whistle-blowers only adds to the realisation that no such public scrutiny of the costs and benefits of the NSA programme is currently possible. The fact that most members of the United States Congress, as well as members of the Homeland Security Committee, had little or no knowledge of the programme raises significant questions about who in monitoring it. With the exception of the President himself, to a large degree, PRISM lies beyond the scrutiny of elected officials.

Contrary to Richard Rorty's assertion that religion is a "conversation-stopper," what we should recognise is that, in the current political climate, security has become the real conversation stopper. The absolute that is beyond question now takes the form of the demand to protect the homeland from all threats to its security. Unfortunately, the public cannot be told what these threats are, or what the government is doing to counter them. No longer is the motto in the United States to be "In God we Trust" - but rather, "In the State executive we trust."

Perhaps we should just accept the tragic paradox of this situation? This would seem to be the message of films like Christopher Nolan's The Dark Knight. In that film, Bruce Wayne (Christian Bale) directs Wayne Industries' Research and Development department to build a mass surveillance system to spy on Gotham City's citizens in the hopes of locating the anarcho-terrorist, the Joker (Heath Ledger). When he discovers the existence of the surveillance system, the director of Research and Development, Lucius Fox (Morgan Freeman), warns about the dangers of the device, arguing that it is "too much power for one person." Wayne assures Fox that the system will be used just this once to locate and stop the Joker, and then will be shut down. The moral of the story, as Slavoj Zizek has suggested, is that "our civilisation has to be grounded in a lie - one has to break the rules in order to defend the system." But that is acceptable, because we can trust that our heroes won't abuse the power they claim is necessary for our protection.

But are the fears and doubts some have raised about the PRISM programme necessarily immature and paranoid? Two recent situations complicate any comfortable setting aside of the critical scrutiny of such a question.

In January of last year, two English tourists - Leigh Van Bryan and Emily Banting - sent a tweet stating that they were going to "destroy America" just before they got on a flight to Los Angeles, where they intended to enjoy a week of partying and shopping. Upon arrival, they were quickly arrested, detained, then deported and barred from re-entering the United States. The furor resulted from a misunderstanding of British slang. As Banting told the Daily Mail, "They asked why we wanted to destroy America, and we tried to explain it meant to get trashed and party."

A similar, though less amusing, situation occurred recently in Canada. A Muslim man, Saad Allami, sent a text message to his sales staff in Montreal, urging them to "blow away" the competition while at a trade show in New York. Three days later, he was arrested by the police and held in custody while his house was searched for explosives. His employees were also detailed at the Canadian-American border for hours until the misunderstanding was resolved.

These rather mild examples illustrate some of the potential "collateral damage" that may result from the widespread monitoring of the general population. More sinister errors still are imaginable, and this does not yet address the possibility of intentional abuses of the system.

In the context of a different discussion, Glenn Arbery has suggested that, what was once said of God, is now true of the surveillance State:

Search me, O God, and know my heart; test me and know my thoughts. See if there is any wicked] way in me and lead me in the way everlasting. (Psalm 139:23-24)

Such a realisation demonstrates the ongoing relevance of Carl Schmitt's well-known observation that "all significant concepts of the modern theory of the State are secularized theological concepts." According to Schmitt, however, the implication of this understanding is that liberal democracy is unrealistic and doomed to failure. What, then, of calls to trust our democratically elected governments? If Schmitt is correct, the sovereign State cannot effectively execute its function of establishing for itself exceptions to the rules that citizens must obey, if the citizens themselves are able to challenge the sovereign's authority. This raises the question of whether citizens in democratic societies should be so quick to put their faith in the emerging political theology of modern State surveillance.

When Rorty accused religion of being a "conversation-stopper," he did so because he believed that references to religion bring an end to any debate, because it defers to an unquestionable sovereign being whose authority has to simply be taken on trust. If it is now the State, rather than God, that we are to entrust as our guardian and confessor, while the details of what it does to protect us must remain "ineffable" and beyond the knowledge of mere mortals (the average citizen and their elected representatives), then surely the terms of such a "covenant" need to be carefully and transparently negotiated.

The President has said he would welcome a debate over the scope of surveillance - does that include the drone programme? - but shows no interest in initiating one. Without such a transparent public discussion, there is reason to worry that the new god of "Security" will soon reveal itself to be little more than a Golden Calf.

Christopher Craig Brittain is Senior Lecturer in Practical Theology in the School of Divinity, History and Philosophy at the University of Aberdeen. He is the author of Religion at Ground Zero: Theological Responses to Times of Crisis.