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The Abu Ghraib stuff was disgraceful to the U.S. but it was not the equivalent morally or physically in terms of what Nazi era Germans did, or of what is done by current represive regimes, various head chopping islamic terrorists and relatively recent genocidal actors in places like Rwanda. We are also not "better" or "above" these people.
That said, Abu Ghraib was definitely bad and heading toward badness more in the league of the stuff mentioned above. It is to our credit that our own public outrage brought it to an end before it got there. It is not to our credit that we've let the leaders slide and just punished chumps like Graner.
Chumps like Graner do need to be punished though, and hard. It helps other people remember, even if they find themselves part of a mob or an Abu Ghraib interrogation staff, that there is a moral universe outside the mob or prison. It might help a few people opt out of the mob or blow the whistle on it.