I don't think it compromises their ability to go after others so much as it dilutes the motive. I agree with this essay; when I hear someone was "tortured" now I think it could mean something as trivial as being kept awake for 24 hours, or being punched a few times. And these are bad things, but it doesn't send shivers down my spine the way the word "torture" used to.
Whatever you call it, the abuses at Abu Ghraib were illegal, and the perps were prosecuted and conviced by military courts.
I think that means what happened there was against the law, don't you?