What would you say was supposed to be the message and overall meaning behind this movie?

From gruesome child sexual abuse followed by murder, to having the supposed innocent black male suspect confess under threats and coercion, to there being a retired Professor trying to help him, to another serial killer being in the cell etc, to the seemingly anti-death penalty stance but then when his family is in trouble, the professor has to confront the killer by himself etc etc, to the gruesome past incidents of prison violence...

What is the overall message of "Just Cause" (1995) cheers.

P.S. Why are prison inmates so violent and even if they did think the guy was wrong and guilty, why did they decide to, spoilers alert, attack his genitals like that, and are we, as audience, supposed to think of them as being purely in the wrong or potentially understandable but having crossed a line, and if they know its likely to make matters also worse, why do they bother playing at vigilante "heroes" in the first place? Or are they just being selfish and wrong and having a vain attempt to prove who is boss, maybe prison is capable of making others more prone to brutal violence etc (yes, I am talking about that twist towards the end)?