In his new book, No Place to Hide, Glenn Greenwald tells how Edward Snowden once confided to him, "with a hint of embarrassment," how much he had learned from playing video games. In the black-and-white world of video games, "the protagonist is often an ordinary person, who finds himself faced with grave injustices from powerful forces and has the choice to flee in fear or to fight for his beliefs," Greenwald writes.

But Edward Snowden's video-game world is not the real world. I see Snowden in a very different light. My colleagues and I spent our careers in the CIA looking for people like him—on the other side, that is. We worked hard to locate the kind of person who could be persuaded to give up his country's secrets: narcissistic, often delusional under-achievers whom we could hope to turn into loose-lipped sources in our enemies' camps and other hostile locations. We understood just how valuable it was to every aspect of our foreign policy to know the plans and intentions of our enemies; the best way to do this was to look for a source and exploit people like Snowden, the National Security Agency leaker, ­ to target for this purpose.

The Russians weren't slouches either in searching for sources of classified information. They were looking for their Snowdens too. You don't have to go back too far to see their success in recruiting American spies with unique access – John Anthony Walker, Aldreich Ames, and Robert Hanssen – who did immense damage to our national security. Moreover, Ames and Hanssen's compromises led to the death of many of our top Russian sources. Walker's compromise, by contrast, allowed the Soviets to know the locations of U.S. submarines around the world. One shudders to think what more could have been done against us if they had had Snowden's access to sensitive communications and his technical know-how on how to extract it from the system. Some people think of Snowden as a latter-day Daniel Ellsberg, a noble whistle-blower. Clearly I do not.

For those who believe that the United States should step back from its engagement from the world, toning down our robust national security and dramatically shrinking our defense and intelligence community, Greenwald's rationale and Snowden's behavior might appear to vaguely honorable. And in this next round of debate, the emphasis will once again be on the domestic side of Snowden's disclosures, as opposed to the enormous international damage done to our country's self-defense by his revelations.

The picture looks different for those who believe, as I do, that the world is still a very dangerous place and that America faces grave challenges from a range of threats as it plays its essential role as guarantor of global peace: terrorism and instability across the Middle East; China's military muscle-flexing in Asia; and Putin's imperial designs in Ukraine and potentially towards other neighbors. From this perspective, Snowden's actions are deeply troubling in that they directly caused a serious loss of capability to understand the plans and intentions of current and future adversaries. Snowden single-handedly blinded us to critical targets and eliminated our ability to see what some of the key players on the international stage are up to. From first-hand experience, I can state unequivocally that the capability to do this comes at incredibly great cost in time, money and personal sacrifice.

As James Clapper, the director of national intelligence, told the Senate Select Committee on Intelligence in January, Snowden's disclosures constituted "the most massive and damaging theft of intelligence in our history." He added that "we've lost critical foreign intelligence collection sources, including some shared with us by valued partners. … Terrorists and other adversaries of this country are going to school on U.S. intelligence sources, methods and tradecraft, and the insights they are gaining are making our job much, much harder."

This is a very hard subject for government officials to talk about without compromising additional capabilities (even this article had to be approved by the CIA's Publications Review Board). However, only a cursory reading of our history reveals just how important gaining access to the dispatches of our enemies has been in every war since the American Revolution. Moreover, this activity has been authorized by all of our presidents since George Washington. Protestations aside, every nation uses its technical collection capabilities to the maximum in the international arena, and will continue to do so as long as international conflicts are with us. No one should doubt that our adversaries and some of our fair-weather friends are cheering the loss caused by Snowden.

But, to give the devil his due, let's look at Snowden's domestic revelations about U.S. citizens' privacy, which have drawn most of the attention and concern from the American people. It is eminently clear that the intelligence community, Congress and the White House are struggling with the double-edged sword of privacy and national security, particularly as technology progresses at unprecedented speed. And I am reasonably optimistic that, despite the public hand-wringing, they will quickly come up with the right balance that protects our civil liberties and doesn't cripple our intelligence collection against our enemies, who do, at times, operate in and cooperate with U.S. citizens. When the news cameras stop rolling, these officials all know just how vital these collection platforms are to our defense while at the same time truly appreciating the value of the law and the importance of protection of our citizens' rights. Nevertheless, implementation won't be an easy task, and it certainly won't take place above the requisite Washington self-serving politics.