During The Shawshank Redemption, why do you think Brooks cannot hadle his freedom, saying that he "can't make it on the outside?"
and why do you think the prison guards and the warden believe that it is acceptable to treat the prisoners the way they do?
This is a great question and I think we can say two things. First, one of the things that Red and Brooks often said was that men become institutionalized. All they know is the prison system and that is it. In other words, some people spend so much time in prison, they do not know how to be free. This is a profound theological point, if you think about it. Freedom can be a scary thing, because now you are responsible for your life.
Second, another theme of the movie was the idea of hope. Andy never lost hope. This is why he concocted an escape, but the other men did lose hope. In fact, Red rebuked Andy by saying, "don't give hope to people." For Red, hope was a dangerous thing, because to hope for something that you would never see (in this case, freedom) is cruel. The point is that without hope you can't really live. Brooks was in prison so long, he lost hope to live on the outside. So, when he was free, he still had no hope. He could not handle it. So, he killed himself.
I will add a summary of the thoughts of Peter Berger. His work will help greatly.
Regarding your first question, I'd take a look at Dostoevsky's "The Grand Inquisitor" for a good parallel on this topic of freedom. In that story, the Inquisitor argues that freedom is evil in itself because it makes evil possible in the first place. Sure, good is also made possible, but the point is that we would have no need for the terrible struggle between good and evil if freedom did not exist. Brooks cannot handle the anxiety of this struggle, so he "can't make it on the outside."