Torture is said to be neccesary to the "war on terror", as is locking suspects up for long periods without benefit of a trial or even a hearing. To be neccesary however a thing needs to be helpful to the purpose in question and obviously to be helpful it must not be counterproductive. So are such measures counterproductive? I believe they are, for they keep interogators from the one thing they need for a successful interogation. That is of course someone who knows something to reveal.
To understand why that is understand what starts most investigations off. While in the movies of course vigilant police and spies spot bad guys doing something bad and pursue, in fact this is fairly rare. In fact most cops don't come across a robbery or murder EVER in their careers. Almost all criminal and anti-terrorism investigation starts with someone in the public telling the police of something suspicious. Now obviously most of the people that give such information have some relationship the suspect. After all how else do they know of the things they find suspicious? They might be relatives, neighbours, friends, coworkers or even lovers. They will therefore have a natural sympathy for the suspect, as they have some relationship to him. They obviously don't want to have him sent away for two weeks on nothing but a suspicion, or tortured or otherwise subjected to humiliation, pain or loss of liberty. If the alternatives are these or letting him continue with suspicious behaviour they will tend to do the latter. There is always a plausible explanation for suspicious behaviour. The man buying diesel fuel might have a friend with a tractor or an emergency generator. He might be buying fertiliser for his back garden etc. The potential informant will make his excuses for not acting. Over 90% of the time these excuses willl be right. Far more people buy diesel feul to feul things than to blow things but. Most for Capability Brown purposes not Guy Faux purposes. But a tiny percentage of the time the suspicions will be right. Those that suspect but not enough to potentially subject their friend to torture will end up saying "I shoulda..." which is no help to the widows of their brothers victims.
This is not their fault though. Most would gladly have reported their suspicious if the result would have been a civilised investigation that didn't torture the suspect or ruin their life by "disappearing" them for a fortnight and not letting them tell people where they are. The fault for the lack of information is the government's for substituting brute force and illegality for allowing the community to trust them. This effect is even more powerful if no one person has enough information to trigger an investigation. If Achmed knows that Mohammed, his coworker, is do something alarming, and his sister Fatima knows something else susicipious, and his neighbour is aware of a third suspicious thing, it might take all three pieces of information to justify an interview, search etc. that would avoid catastrophe. So the probability of preventing it is a power in this case 3 of the probability that each person would report him. This second probability will go down sharply with each increase in arbitary power the suspect is subject to and thus the first probability will go down even faster.
Violating the rights of the accused only serves to reduce the number of people who will be accused, save by people who bear them ill-will. Accusations based on honest suspicion of a person's actions, the only reliable guide to possible wrongdoing, will decline. This is a blow at the heart of our ability to conduct the War on Terror.