Personally, I think torturing prisoners is a bad idea because if you do it, then Al Qaeda might as well win, since it means you're as bad they are. Realizing that's not a conclusive argument for everyone, some of whom would rather be evil than slightly scared, I present a round-up of people giving another reason why it's a bad idea. It doesn't work. The people saying it doesn't work aren't J Random Commie or Johnny Arab, either. They're the CIA, the FBI, American army bods, US government officials and so forth.
It's a handy cut-out 'n' keep guide to why it shouldn't be in the interrogation arsenal.
Washington's Blog: Why We Need Torture to Keep Us Safe
Title from Frank Zappa's The Torture Never Stops.