That's true, but there is strong evidence that while people prone to commit crimes are in jail that are not, simultaneously, outside of prison committing more crimes.
You and me didn't read the same article, or the same HN thread.
The guys in the SHU are in one of the highest security prisons and, still, they managed to stir a huge prison strike and (If you believe the article) lead a criminal empire that extends its influence far from the prisons.
So, point me to that "strong" evidence, and make it peer reviewed, if possible.