If the Catechism can't be used to say torture is only wrong if it is used "to extract confessions, punish the guilty, frighten opponents, or satisfy hatred," can it at least be used to say that torture is only torture if it is used for one of those reasons?
In other words, can it be interpreted as defining torture as "the use of physical or moral violence to either extract confessions, or punish the guilty, or frighten opponents, or satisfy hatred," with the implication that the use of physical or moral violence for any other reason isn't torture, and therefore isn't covered by the many, many ecclesial statements that torture is wrong?
The reason it can't be interpreted along those lines is simple: It's not a definition consistent with any known concept of torture.
Consider this question: Is the use of thumbscrews on a prisoner, to the point of leaving him writhing in pain, torture? If the above interpretation [that the Catechism defines torture in reference to an exclusive and precise list of reasons] were valid, then the answer to that question would be, "It depends."
But no one thinks the answer to that question is, "It depends." So if the above interpretation were valid, the Church would be redefining a term in a way inconsistent with every other usage of that term, offering this idiosyncratic (to say the least) definition in one place only, sandwiched between mention of terrorism and amputations, neither of which it defines, and then (according to the interpretation) using the word equivocally -- without so much as a hint that there is a bizarre and inconsistent definition -- in the Compendium of the Catechism, in local catechisms, in papal speeches, in letters to Congress.
All of that is absurd. Therefore, the idea that the Catechism is defining torture in a restricted sense is also absurd.
If the Catechism isn't defining torture, though, what's all that stuff about "to extract confessions, punish the guilty, frighten opponents, or satisfy hatred" doing there?
It seems to me that it functions, not as a formal definition, but as a working description of torture. As a description, it characterizes torture without specifying it. It states the sort of thing torture is and the sorts of things it's used for, in general terms that are nevertheless sufficient to show that torture is not simply any sort of real or perceived mistreatment or punishment.