Sorry, but you lost me at evil.
Good, evil, right, wrong - black and white terms for people who see the world as one or the other. One root thing is assigned a value and anything connected to it falls under that same value. There's no room for intent, only absolutes. This is why I can't debate on this forum. "You're either 100% with us or against us."
evil in the world. Whether there are genuinely, irrevocable evil people, I don't know, but there are evil, evil deeds. (I would hold the case of Baby P up as an example.)
That said, you asked about the trade-off between bad information, good information, and varying interrogation techniques. What you're asking about is essentially a value, a personal belief that is held sometimes without logic. I personally don't believe it is ever
right to torture another human being. Causing permanent physical and mental damage in someone because you think they might know something useful which may or may not help you - it's unacceptable in any situation.
You asked, I answered, and I'm happy to discuss - but if you try to debate it with me, I'm going to ignore you. There are some values that can be evaluated, discussed, and examined, but sometimes they really do come down to "I believe this is just wrong."
Another example, just to throw it out there, would be the hypothetical statement that, "I believe killing someone is wrong in any circumstance." Now, the person may think that killing in self-defense is one of those situations where it's wrong but you can't do much else. The person may believe that someone who got the death penalty deserves to die; the values are not mutually exclusive. But some things do come down to a moral judgement that something is wrong to do to another person, an animal, whatever.
This is one of those debates that is tangled in morals, which makes it extremely difficult.