It may be true that individual torturers are sadists, or the policy-makers seek to terrorize populations of people. But torture is primarily an information-gathering tool for the US, as a matter of policy. It's an information economy. And the individual prisoners are the aggregate bits of data that comprise the information-gathering tool. The justification comes a priori: information is good; information in the name of the defense of civilization is better. But torture information is an odd entity in that much of the framework narrative of what is sought through torture comes a priori as well. Bits of data make no sense otherwise. They're meaningless bits of data. Those bits have to fit into a background framework of interpretation, beliefs, assumptions, values, goals, etc. for them to come to make sense. But the information from one torture victim is unlikely to have much useful meaning.Now take a look at this guest-post in the Washington Note by Lawrence Wilkerson, Colin Powell's Chief of Staff as Secretary of State (via Scott Horton). Wilkerson discusses what the media has missed in their portrayal of Guantanamo Bay.
For torture to be effective as an information-gathering method, it has to be institutionalized and used broadly. This is what I mean by aggregation. The information comes from observation of patterns generated by aggregating what the individual victims say and less from the words of an individual torture victim. Meaningful information from torture necessarily comes from torture's institutionalization. Some information is easy enough to verify: you can indeed verify where an individual torture victim says a weapons cache is by going there and finding the weapons or not. This kind of everyday use of torture, however, hasn't been part of the American (liberal) justification of torture. It's too small-scale and doesn't rise to the level of moral urgency of the ticking time bomb scenario, for example, which is the image the institution uses to justify morally its existence. But, while you could possibly verify concrete things like a weapons cache through torture of one person, you can't verify an alleged plot and its full details without torturing broadly and collecting the bits of information - sorting out the consistent from the inconsistent - into a patterned narrative.
...the ad hoc intelligence philosophy that was developed to justify keeping many of these people, called the mosaic philosophy. Simply stated, this philosophy held that it did not matter if a detainee were innocent. Indeed, because he lived in Afghanistan and was captured on or near the battle area, he must know something of importance (this general philosophy, in an even cruder form, prevailed in Iraq as well, helping to produce the nightmare at Abu Ghraib). All that was necessary was to extract everything possible from him and others like him, assemble it all in a computer program, and then look for cross-connections and serendipitous incidentals--in short, to have sufficient information about a village, a region, or a group of individuals, that dots could be connected and terrorists or their plots could be identified.A couple of other pieces on the torture regime are worth your while. Mark Danner's NY Review of Books review of the 2007 ICRC Report on the Treatment of Fourteen "High Value Detainees" in CIA Custody. (You can see the original report here, among other places). And a brief discussion of Obama's torture policy by Andrew Sullivan.
Thus, as many people as possible had to be kept in detention for as long as possible to allow this philosophy of intelligence gathering to work. The detainees' innocence was inconsequential. After all, they were ignorant peasants for the most part and mostly Muslim to boot.