All the prisoners who wanted to kill/rape Miranda/Talia and killed Talia's mother were murdered in revenge by the League of Shadows on Ra's al Ghul's orders, recompense for the murder of his beloved wife (remember the only thing that satisfied him in Batman Begins was "revenge"). All the prisoners inside the prison, other than the doctor (who was blinded and left there as punishment for the mess he made of Bane) were said to be enemies of Bane, left there in the prison to suffer and lose hope and die (he expected no one to get out, not even Bruce, making him lose hope and eventually break from seeing his city destroyed).
The original prisoners seemed to go out of their way to attempt to keep anyone from escaping (see their mauling of Bane and attempting to murder Talia as she tried to escape), while these prisoners chant in support of his climb and escape. They feed him and keep him alive (though the helper does say they paid them to do that), but Bruce is about justice. He doesn't believe leaving these people in a hellish prison to suffer is the right thing. Bruce even said in Batman Begins that he sort of lost the focus on the simplicity of good and evil and he understood how it was to be a criminal. So was it really his duty and right to leave them behind to suffer and die?
That might not be the most perfect answer, but he believed in the system, something that Ra's al Ghul and now clearly Bane scoffed about (Ra's as Ducard questioned his faith in "corrupt bureaucrats") while both Bane and Ra's simply acted as judge, jury and executioner, something that Bruce disagrees with.