I'm not sure what they did to this guy at Guantanamo, but whatever it was, it worked.
There's no question that some techniques used at Guantanamo, like sleep deprivation, Metallica at 100 decibels for hours, and especially waterboarding, border on torture. Not to mention all the psychological stress they must be using.
The question, as always, is does the end (=learning about lots of plots, foiling them, saving perhaps thousands of innocent lives, arresting more terrorists) justify the means (denying Khalid Sheik Muhammed the most elemental of his human rights)?
My answer, I suppose, is that it depends on the end and the means. In this case, I think the end in question does justify the means in question, basically because KSM is who he is. Everyone knew he was guilty as hell all along.
(Yes, I've heard the slippery-slope argument, and it has a lot to be said for it. We start out by forcing KSM to listen to "Enter Sandman" at 100 decibels for a week nonstop, and wind up like the Gestapo and the KGB with a Gulag of our own. It's a genuine concern. My response, I suppose, is that I don't think we've slid too far yet. An example of too far is Abu Ghraib. That wasn't anything like Guantanamo, in the sense that whatever goes on at Guantanamo is done on orders by higher authority, eventually reaching up to the President, while Abu Ghraib was a unit gone bad. But the sadism and perversion of the Abu Ghraib torturers, mixed with the fact that the people tortured there were small fry, clearly is far beyond the limit at which the end justifies the means.)
It sort of reminds me of what was effectively the US assassination of Admiral Yamamoto in 1943. Our intelligence learned that he was going to be flying from Point X to Point Y on Day Z, and our fighter planes were sent to blow him out of the sky. They did. Admiral Halsey's reaction was, "What's so good about that? I had hoped to lead that bastard up Pennsylvania Avenue in chains."
I think KSM is just as much an enemy combat leader during wartime as Yamamoto was, and deserves no better. Yamamoto pulled off Pearl Harbor; KSM pulled off 9/11. He will, of course, be executed after his military trial, I have no doubt about that.