I'm of the opinion that torture isn't completely ineffective. Its definitely not as effective as Hollywood or the Amerikkkan military likes to pretend, and as you said, it can harden the victim or lead to them saying anything to get out of the situation.
I also know that the Soviets didn't torture people as widely as most anti-communists believe, and I do agree that torture is very abhorrent, and while I can respect the moral and practical arguments against it, I think that completely disavowing torture is almost as big a mistake as using it whenever you want all willy-nilly.
Some scientific papers do note that torture can be effective in certain contexts, and torturing enemies for information is probably a multiple-millennia old tradition, and I find it very hard to believe that it would be kept in practice if it wasn't useful at least some of the time.
One reason and one only: torture is self-defeating. Torture is universally understood by people who have basic empathy as something Bad People do. (That's why when it was revealed that the US had torture as SOP in their black sites, people would automatically say "The US does not torture" because they couldn't square with reality and needed to repeat the lie to themselves.)
It doesn't give reliable intelligence, and hardens the individual and anyone associated against what you are trying to communicate. Critical support for Vietnamese comrades, but using torture played into the hands of the imperialists by giving them an easy way to say "Look! They're the bad guys!"
I'm not of the opinion that one has to "play nice" but using torture is always a bad move.
Edit: corrected a word.
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