Torture's real purpose, however, instead of or in addition to the purpose of extracting information, can better be described as terroristic. That is, it primarily functions to intimidate "people other than the victim". In other words, there's a message being broadcast to actual or potential enemies: Don't Fuck with Us.
There are few, if any, clear cases of a regime's voluntarily renouncing terror after having created, through terror, a situation in which terror was no longer needed. And there is considerable evidence of the improbability of this sequence. Terroristic torture tends to become, according to Amnesty International, "administrative practice": a routine procedure institutionalized into the method of governing. Some bureaus collect taxes, other bureaus conduct torture. First a suspect is arrested, next he or she is tortured. Torture gains the momentum of an ingrained element of a standard operating procedure.
Several factors appear to point in the direction of permanence. From the perspective of the victim, even where the population does not initially feel exploited, terror is very unsuitable to the generation of loyalty. This would add to the difficulty of transition away from reliance on terror. Where the population does feel exploited even before the torture begins, the sense of outrage (which is certainly rationally justified toward the choice of victims, as we have see) could often prove stronger than the fear of suffering. Tragically, any unlikelihood that the terroristic torture would "work" would almost guarantee that it would continue to be used. From the perspective of the torturers, it is rare for any entrenched bureau to choose to eliminate itself rather than to try to prove its essential value and the need for its own expansion. This is especially likely if the members of the operation are either thoroughly cynical or thoroughly sincere in their conviction that they are protecting "national security" or some other value taken to be supremely important. The greater burden of proof rests, I would think, on anyone who believes that controllable terroristic torture is possible.
Henry Shue, "Torture", Philosophy and Public Affairs, Vol. 7, No. 2 (Winter, 1978), pp. 124-143.