Mr. Fox, a British Conservative, is a member of Parliament and former secretary of state for defense.

Peace and security are not the natural state of affairs. It is a fact of life that many of those who live comfortable middle-class existences in affluent, liberal, pluralistic democracies in the 21st century seem to have forgotten. Those who live without a full grasp of the risks and sacrifices taken by others on their behalf will not understand the constant battle for law and freedom against disorder, anarchy and terror. Just as a gardener fights a constant war against untrammeled nature, but casual observers see only order and tranquillity, a constant struggle is being waged against the forces of disruption and destruction so that we can take the safety and security of our daily lives for granted.

For our intelligence services to operate effectively, and to protect us from these threats, they need to be able to do things in secret, secrets whose public disclosure would be damaging to our national interests. We depend on the legal and moral partnership of our governments and the employees and contractors it uses to maintain the confidentiality of these secrets. Yet all of this has been imperiled over the past 10 months by the slow public parading of intelligence secrets stolen by National Security Agency contractor Edward Snowden, working with Guardian journalist Glenn Greenwald and others. As recently as last month secrets were still being spilled, this time about an NSA malware program.

What are the size and scale of our intelligence agencies that so agitate their critics? In the case of United Kingdom, it is around £2 billion a year. Put another way, this is less than 0.3% of total government expenditure or the equivalent of how much we spend on the National Health Service every six days.

For the U.S., the comparable figures are 0.7% of total government spending, around only 5% of the defense budget.

Edward Snowden speaks about surveillance in a videoconference with European officials in Strasbourg, France, April 8. frederick florin/Agence France-Presse/Getty Images

One criticism that has been frequently leveled at the activities of the security services is that their decision-making and operational planning is done in secret. This is one of the most ludicrous criticisms of all. The reason that these activities are kept secret is not because our agencies are embarrassed about them or want, intrinsically, to keep them from the public, but because they need to be kept from the terrorists, foreign agents and proliferators who pose the threat. Were such decisions and operations to be carried out in the full glare of the public gaze, then the sometimes fragile operational advantage will be lost, leaving us all more vulnerable.

As a result of Mr. Snowden’s activities and the information that has now become available to our enemies, we have seen terrorist groups in the Middle East, in Afghanistan and in other parts of South Asia, discussing the revelations in specific terms, including the communication packages that they have used up till now and those that they will move to in the future, now that they know how they have been monitored. We have actually seen chatter among specific terrorist groups, at home and abroad, discussing how to avoid what they now perceive to be vulnerable communications methods and, consequently, how to select communications that they perceive not to be exploitable. No doubt these terrorist groups are extremely grateful to Messrs. Snowden and Greenwald and their accomplices for these useful tools in their war against our citizens, our armed forces and our way of life.

Not only did Mr. Snowden show how the NSA intercepts emails, phone calls and radio transmissions of the Taliban in Pakistan; he also revealed email intercepts regarding Iran and the global tracking of cellphone calls looking for unknown associates of non-intelligence targets. Mr. Snowden also told the South China Morning Post about how the NSA hacks into computers and mobile phones in China and Hong Kong. His labors were designed to purposely damage American diplomacy and its relations with some of its closest allies, including the United Kingdom and countries such as Norway and Sweden. All this is in line with the virulent anti-Western, and particularly anti-American, views of Messrs. Snowden, Greenwald and their malicious associates.

It remains to be seen just how much damage has been done to the West’s security architecture as a result of the Snowden disclosures; much of this information would be classified. There has been speculation, however, that the ability to anticipate Russian intentions in relation to Ukraine and Crimea was diminished as a result of having to close down potentially compromised signals-intelligence capability. If true, this would be the first practical demonstration of how Mr. Snowden and his acolytes had successfully damaged security to the benefit of Vladimir Putin‘s regime.

The public justification given by Mr. Snowden for his actions was “I don’t want to live in a society that does these sort of things”—surveillance of its citizens—”I do not want to live in a world where everything I do and say is recorded.” So where does he choose to go? Russia. In a bizarre and perverse video statement in October, he said of America’s intelligence techniques: “They hurt our economy. They hurt our country. They limit our ability to speak and think and live and be creative, to have relationships and to associate freely.” This from a man who is snuggled up with Mr. Putin’s henchmen.

Edward Snowden thinks of himself as a cyber-age guerrilla warrior, but in reality he is a self-publicizing narcissist. He did not find or expose anything illegal, nor did he exhaust all legal and constitutional options to express his reservations about the intelligence and security services. He did not attempt to limit any potential damage in making his point. He did not show that any agency activities were unreasonable in law. Let us not imbue his cowardice with higher motives. Let us not confuse his egotism with public service. Let’s not call his treachery by lesser terms. Let us be clear about the intent and impact of his actions. Let us be clear to the American people and their allies about the threats they now face from enemies inside and out, terrorist and criminal. For once, let’s say what we mean. Let us call treason by its name.