Why good people do bad things
I think these two may apply to Abu Ghraib
The pressure to conform.The pressure to conform is powerful. When a group engages in unethical behavior, individuals are far more likely to participate in or condone that behavior rather than risk standing out.
Obedience to authority. It’s quite difficult for most people to ignore the wishes of those in authority positions. People also feel like they’re less responsible for wrongdoings if they act under the direction of someone else. Both of these reasons explain why employees are likely to act out the unethical wishes of their supervisors—and feel far less guilt than if they had decided to do it themselves.
It doesn't really excuse the people who tortured, but it certainly puts a lot of responsibility on those in charge, as well as on regulations and inspections.
The danger is that when your President tells everyone openly that he thinks torture is effective, then you feel justified in using it.