I agree on all your points.To the psychotic, and those looking to get someone to say certain things regardless of truth i am sure torture is effective. I was speaking moreso of generally non evil people in power attempting to find a use for torture ( or rather , the threat of torture.).
Though i have always wondered, why not just say the person said it? Even if i didn't care about torturing someone, it seems a lot of work and mess to go through to get them to say something i could say they said anyway.
I first saw that device in the game aptly named Amnesia: The Dark Descent. Pretty good game that shows how one can start torturing people.
Well, at least in the middle ages, the problem was that they basically haven't yet figured out justice. Unless the criminal confessed, they hadn't figured out how you can convict based on witnesses and experts. To be sure that he did it, you had to have either (A) a confession or (B) some trial by ordeal in which supposedly God would prove if they're innocent or not.
Using torture actually went up in the Renaissance, when judicial divination or trials by ordeal fell out of favour. Suddenly you couldn't say "he did it because he pulled the short straw" or respectively "he did it because he couldn't get a stone out of a pot of boiling water."
Compounding it, is the problem of humans being unable to admit they could be wrong. They get some gut feeling or intuition that X must be guilty, so then he _is_ guilty, and all that remains is to somehow make it so. So they're not really looking to really prove or falsify that X is a witch, or Y is a highway robber, or Z conspired with the enemy. They already _know_ it, evidence and reality be damned, and all that remains is to beat him or bribe someone to be a false witness, and confirm that.
It's something that continues to this day, e.g., in the form of cops planting evidence. Most are probably not even thinking of it as being a bad cop or the kind of villain who's getting someone executed for personal gains like fame and promotion. They _know_ he did it (even if he really didn't), they just have to make the accusation stick.
Third is the problem of, basically, groupthink. Think, "you're not supporting the troops" or "if you don't do X, the terrorists win." They thought the same in the middle ages and renaissance too. They had to do _something_ or Satan wins. They had similar rationalizations, e.g., in the form that only a witch would feel pity for a witch (so if you refuse to torture her, you're practically swearing fealty to Satan himself), or only a traitor would feel pity for a traitor (ditto.)
Fourth, well, basically plain old sadism by psychopaths in power. For some people the goal isn't even to extract a confession, but to cause pain.
E.g., Stalin's regime devolved to such extremes as beating someone black and blue before executing them. And not even a public execution and deterrence value. People whose execution would be seen by at most a handful of people, were stripped down and savagely belted before being dispatched with a bullet in the head. In a twist of poetic injustice, even NKVD heads who delivered such torture, were given it when they themselves were purged. E.g., Yagoda got stripped and beaten black and blue before his execution by his successor Yezhov, which in turn would be stripped and beaten black and blue before his execution by his successor.
If you think of it, it's as pointless sadism as it gets: there was no more confession to extract, no lesson to teach to someone who'll be dead in the next few minutes, no half-way sane goal or purpose. The only purpose was to cause some more pain while you can.
Even as means of extracting confessions, they knew that other stuff like waterboarding is quicker and more reliable in getting someone to confess any enormity you wish them to confess. But the directive was still to beat them. That was the real goal. Not even to extract a confession, but to beat people up.