Of course it does – some of the time, and, I would guess, often. Sometimes the mere threat of it is enough; witness Galileo. When it doesn’t work, the poor bastard becomes a hero : France’s champion French Resistant, Jean Moulin, or – presumably – John McCain in Vietnam. The Catholic Inquisition continued to use it, not only because it punished heretics and witches who deserved the pain and punishment anyhow, before they suffered the ultimate torture of being burned alive at the stake, but because it forced them to renounce their “errors” and provided the Church with the names of other “criminals”. The Americans in Irak and Guantanamo, the French in Algeria, the Russians and Germans in World War 2, and probably every other nation at war or under threat, found that it was, and is, a precious provider of vital information.
It works. But should we allow it to be used ? The Geneva Convention says no. The Law says no. Fundamental human decency says no. But faced with the credible situation of suffering or death threatened to loved ones unless the prisoner, already without fingernails if not fingers, spills the beans, it is hard to blame him for giving in.
The question is not whether it works, or even whether it is legal. It is an abomination such that having a President who publicly condones it, has itself become more than civilized citizens can stand.