...And over-reaching, they fell flat on their faces
Maltreatment of prisoners is a "bad thing" for a number of reasons:
 It's just plain "bad" to mistreat people who are at your mercy. You know, the "ethics" and "morals" thing.
 Mistreating prisoners does not actually make them more willing to talk. In fact, even hard-core physical torture has been shown to be counterproductive to interrogation - people being tortured (and, by extension, mistreated) will say anything they think will get the torment to stop. Not necessarily the truth, but what they think their captors want to hear. This does not lead to "good intelligence".
 Even the Nazi SS troopers found that torturing (and killing) helpless people takes a toll on the psyche of the people involved. People who have been involved in torture (and, by extension, mistreatment) often become less effective at their other jobs and in interpersonal relationships.
 Having a reputation for humane treatment of prisoners makes the enemy combatants more willing to surrender. A reputation for harsh or cruel treatment leads soldiers to "fight to the death".
 No matter how manifestly unfair it may seem that we have to be the "good guys" while the other side gets to blow up children, behead reconstruction workers and assassinate doctors and nurses, it's the side we chose to be on.
These are all very good, cohoerent arguments against mistreatment and torture and you'll notice that none of them involved comparisons with Nazis, Soviet Gulags or Pol Pot. This is actually a good thing, since the prison camps at Abu Graib and Guantanamo Bay don't really compare.
The Nazis killed over 9 million people in their prison camps - mostly Jews, but a number of other ethnic groups as well. The Soviets - under Stalin alone - killed over 3 million of their own citizens in the Gulags. Pol Pot, not as good a record-keeper as the Nazis or Soviets, killed between 1 and 3 million people. As you can see, Abu Graib and Guantanamo Bay aren't in that league at all. And that is exactly what people are going to say in order to redirect attention away from what is happening and onto the people (e.g. Senator Durbin) and groups (e.g. Amnesty International) who are overstating their position.
The problem with trying to over-reach your position is that you stand a good chance of falling on your face.