Well, I got to figure that with the nuke example, with the stakes that high, I really don't have much to lose. Maybe the torture won't work, but there's a chance that it might, and the bomb can be stopped. If we don't torture him, there's no chance. It's as good as if I set the bomb off myself.
Either way, I've got the blood of at least one person on my handsI just have the chance to keep the blood of 999,999 others off of them.
Of course, there's also the Realpolitik take on the situationstopping the bomb might prevent a nuclear retaliation on the terror group and/or any country that was harboring them, which could conceivably be much MORE than a million people. Especially if there was a risk of word getting out that a government agent had the chance to get information out of the terrorist that could have stopped the bomb, but didn't, because he thought it would be immoralotherwise, the government risks getting voted out (or toppled) in exchange for the kind of leaders who'd vow to never let that massacre happen again. At any cost.
In practical terms, that'd probably set back the cause of human rights and ethical government action back a lot farther and a lot faster than one would-be mass murderer coming to harm, and then quietly "disappearing."
But where do you draw the line? Would you torture an innocent person if it would save a million lives?
Take this for an example...the nuke terrorist has a five year old girl, who he loves dearly. Who you've also managed to take into custody, and is in the next room over.