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One aspect of this issue (an aspect under-discussed even in progressive circles) is why the U.S. tortures. Torture is useless for intelligence-gathering, but very useful for intimidating and terrorizing populations you want to control --like say in the countries you're occupying.
Not to mention, say, the one in the country you're governing. I think the whole GWOT has been considerably more effective at intimidating and terrorizing the population in the U.S. than the populations that reside anywhere else.