Ok, here is the thing. If torturing (and it sure as hell was torture) potential terrorists was the only way to get the information out of the unsavory fellows, and it had a very high success rate, I'd be in Gitmo right now taking out Al Qaeda eyes with an ice cream scoop. But guess what? It doesn't work. Not any more so than being friendly with the individuals, at least.
Have you ever hold the phrase "You catch more flies with honey than vinegar'? Well in this case it is "You get more information with cookies than waterboarding".
When take a terrorist and slam that man's head into a desk, and waterboard him, and tell him you will kill his family all you are doing is making that individual sure that everything he was raised to believe from birth is true. Americans are devils. They are nothing but torturous, egotistical, immoral brutes who excel at causing pain and suffering to others. You are proving exactly what the brass in Al Qaeda wants their troops to think. Do you really think these men are going to want to go blabbing everything they know to the dirty Americans? Do you think that when they now know that everything they've been told is true, that Allah wants the US destroyed and there are however man virgins waiting for them in heaven that those terrorists are going to back down? It is foolish to think as much.
The only ones who will tell you anything are the mentally weak. And guess what? Al Qaeda doesn't attract too many who are not strong willed and dedicated to their cause. You know that whole part where terrorist members are willing to die for their cause? Do you really, actually think that the bastard enemy pouring some water on them will change their minds? That is foolish.
Look at the interrogations of Saddam Hussein. Do you know how they got him to sing more pretty songs than Elvis Costello and Tom Waits' entire discography put together? They were nice to him. They found an American with middle eastern heritage with the required clearance and had him talk to Saddam. They gave Saddam treats for speaking. It worked.