Nominated for an Oscar at the most recent ceremony, Dror Moreh's terrific documentary on Shin Bet, the internal Israeli security service, can stand beside Errol Morris's The Fog of War as a cinematic illustration of how human psyches bend beneath the pressure of terrible actions.

It would be wrong to say that the six men interviewed, each a former head of Shin Bet, have all turned against the Israeli experiment. But, just as Robert McNamara – engineer of the Vietnam War – offered the subtlest evisceration of American imperial folly in the Morris film, most of the talking heads here reveal how pressing home a hard line only served to soften their own attitude to the Palestinians.

“After retiring from this job, you become a bit of a leftie,” Yaakov Peri, head from 1988 to 1994, explains with a wry twitch. Ami Ayalon, who took over in 1996, remarks: “The tragedy of Israel’s public security debate is that we don’t realise we face a frustrating situation in which we win every battle but lose the war.”

The larger structure of the story will be all too familiar. Success in the Six-Day War of 1967 managed to make Shin Bet’s task almost impossible. Suddenly, close to a million Palestinians, few friendly to the regime, found themselves living within a cobbled-together greater Israel. If any sort of rough order was to be maintained, then Shin Bet would have to abandon many hitherto shakily observed moral principles.

It seems as if George Orwell didn’t really say: “People sleep peaceably in their beds at night only because rough men stand ready to do violence on their behalf.” Nonetheless, the misquote gets at horrible truths about the modern state and its enemies. As we learnt in the aftermath of the Irish peace process, relatively few of those rough men remain unaffected by such violence.

Moreh is to be commended for fashioning such a serious, sober – if occasionally indecently exciting – illustration of these lessons. The six men deserve more enthusiastic congratulations for telling their grim stories.