Very true, but then that's why the aversarial justice system is so important. It's ok for prosecutors and police to use every means legally at their disposal to try and prove someone guilty, as long as that person has an independent advocate with sufficient authority to protect the accused and challenge the prosecution case.
The problem here is that the way these people were treated was perfectly legal and even morally acceptable at the time. Clearly lengthy unecessary periods of solitary confinement, drugs and agressive interrogation without an advocate present should be completely unacceptable. They even used simulated drowning. The paraelells to Abu Ghraib, Guantanamo, the treatment of Bradley Manning and CIA waterboarding are stark. It's pretty clear that these kind of abuses simply do not work.
People subjected to these treatments will say, and even come to believe absolutely anything, so any information that comes out of such processes is worthless. That's completely aside from the deep immorality of using such techniques in the first place. ALl it does is provides moral cover and justification for oppressive regimes to use such techniques completely indiscriminately.