Indeed. The inefficiency of torture has been demonstrated many, many times.
It has also been recognized as such by many, many torturers.
People think torture works because they think that the guilty deserve it. In other words, they want to avenge.
Hence the never-ending rationalization of torture. People want the bad guys to suffer for what they have done.
A long torture represents the worse punishment possible. If the act is bad enough (like 9/11 or rape of a child), many people find it appropriate, and more so if they don't have to do it themselves.
The perpetrators of torture like it. They just need a narrative that justifies it, a narrative they believe in. In that case, quite a large part of us can become torturers if the circumstances put them in the situation.
Many people think that the average Joe would never torture, in any circumstances. It is just untrue. A human just need to be embedded in a group of people which values legitimate violence or torture.
If we have a social support to make it legitimate, most people can do terrible things.
Hence the mobs lynching a suspect - like that guy who was killed in Boston because an online mob pointed him as the perpetrator of the marathon bombs.
Hence the common soldiers of the German Wehrmacht on the eastern front, who participated in the killing of many Jews. The idea that only fanatic Nazis like the Waffen SS or the Einsatzgruppen were involved are just untrue. Many German - who have no issues recognizing their country's responsibilities and atrocities - still can't believe that the average soldier directly participated in the genocide. They did - as historians have demonstrated.
The genocide in Rwanda has also shown that. Most of Hutus' men participated in the genocide of the Tutsis, and most of women either supported it or acted in it.
In a given society in normal circumstances, there will always be people who want violence for itself. Efficiency to solve what the society consider punishable offers the perfect rationalization for their own need to be violent.
If you have an urge to be violent, one can become a cop or join a drug gang. Not that all cops are violent but many are. Many wives of cops or soldiers are beaten by their husband. Sorry to tell harsh truths.
But that can be different. The German police is nowadays known for its specific values. In France, were I live, cops are getting always more violent without any reason for it, just a slow radicalization to far-right ideas and values. More than 60% in the police force now vote for the far-right. This is known through their actual vote when they elect their unions' representatives.
Violence is the norm in most "force institutions" (police, army, intelligence services) in most countries, including democracies. Torture is merely the exacerbation of it in special circumstances where the crime is considered so bad that the uttermost violence is legitimized.
In average, during the XXth century, 90% of casualties during the war were civilians.
When fighting the Germans and the Japanese during WWII, the "good" countries like the USA and the UK went at length to use terror against the civilians - sharing with Hitler the idea that if the people is demoralized by intense bombings, it will force their military to stop the war. Dresden and Tokyo were both bombed with incendiary devices. In Dresden, 130 000 casualties during a sole night, 95% being civilians.
Humans are nor violent nor peaceful by nature. They are social animals who behave according to the current social norms of their social group.
Obama was a splendid President, very respectful of the Constitution - and I gladly voted for him. But he went along with the drone war in Afghanistan, with a large number of collateral casualties. Basically, 5 year-old children of djihadists can legitimately be killed if they happen to be nearby their father when a drone located him. Collateral damages, necessary for the greater good.
The Obamas have become very close to George Bush Jr. They can't stop saying how much a nice guy he is. Except that this guy should be trialed by the International Court of Justice if not by the American legal system for invading and occupying Iraq on fabricated grounds.
How can these super cultivated people and so decent people like the Obamas befriend GWBb Jr? Well, they have been in power as well and that experience has immerged them into the social norms of Washington. Very few are the one capable of keeping a true moral compass while embedded in a specific social class.
I'm no exception to this. I try to be a good guy but I identify myself as the guy in the Star Wars movie who wonders: Are we the baddies?