You think of the story that Glass tells about the inmate who had a huge tattoo on his chest. It extended from his navel to under his chin. It was a huge extended middle finger. Prison guards will tell you that few inmates have dramatic conversions. Usually, things are better for a week or so after Glass' ministry.
Prison is a battle between good and evil.
The men behind bars have a little of each inside their hearts. Wardens will take that. Wardens are thrilled that Glass and his army of volunteers have the courage to go behind the bars, the patience to listen to the inmates. After awhile, the faces of the convicts run together in your mind. Nearly all have had drug problems.