Megan McArdle argues in favor of the efficacy of torture:
One of the most facile dismissals of torture is that it doesn't work, so why bother? That's tempting, but it's too easy. Torture seems to me very likely to work provided that you can verify the information, which I assume interrogators can in at least some circumstances. Nor is it obvious to me that the quality of information is likely to be lower than that obtained by other means: yes, people will say anything to avoid torture, but they'll also say anything to avoid imprisonment. Maybe the lies will be vivider or more voluble under torture, but it doesn't seem necessarily so that the ratio of lies to truth will increase.
For some sense of "necessarily" this may be true, but this flies in the face of historical practice. It seems unlikely to me that torture's most famous systematic applications almost all come in the context of regimes specifically looking to generate spurious confessions. Stalin's Russia, North Vietnamese POW camps, the Spanish Inquisition, it's always the same story. It's not the case, however, that torture "doesn't work" -- Nikolai Bukharin and others confesses to all sorts of preposterous crimes exactly as Stalin wanted them to. The question is whether routinized torture of al-Qaeda suspects is a useful method of advancing any public purpose.
Megan counterproses that "people take the hard stance and say 'Yeah, torture may still work, but we still shouldn't use it because it's wrong.'" I think Megan thinks that people from the "torture doesn't work" camp are arguing in bad faith, but I'm really not. I don't think it makes any sense at all to say that there's a categorical moral against smashing people's fingers with a hammer or whatever other depraved acts of torture you may care to imagine. After all, I believe (as most people believe) that it's sometimes morally praiseworthy for the state to have its agents kill people with bullets, bombs, mortar shells, etc. so there's surely some end such that torturing someone would, if effective, be a just method of achieving that end.
The difference is that despite the horrors of war, there's a very strong argument to be made that if good people systematically disavowed war-making as a practice that bad guys would run roughshod over us. When Hitler's tanks start rolling across Europe, someone's got to shoot back. By contrast, I don't see any examples of societies using routinized legal torture to gain a decisive advantage over their foes or any evidence that the current era of torture has been a net positive in fighting al-Qaeda. To say that a method of investigation works "provided that you can verify the information" is, after all, merely to beg the question. Consulting a psychic works provided that you can verify the information, but spending person-hours chasing down the psychic's "leads" isn't going to make the country safer.