Or possibly you forget. In Abu Ghraib, for instance, people were tortured for the fun of it, and to help bring stability, freedom and democracy to Iraq. Quite noble.

The US tortures to get information about the tortured's friends and allies. "Ticking bomb" stuff. And remember. Same reason McCain was tortured.

The US also tortures the innocent to get confessions, thereby covering the asses of the detaining parties. After all, one doesn't really want to admit to holding hundreds and hundreds of innocent people at Guatanamo, does one? Get 'em to confess to something, anything. After all, they are by definition "badguys" and the US is, by definition the "good guy". Anything that's done to them is just fine.

Those are a few of the reasons. I suspect they will jog your memory and help you come up with more.