For a long time we used to ask if prison helps prisoners to re-insert in society or not. Some people defend that prison can help and others think the opposite.
It is true that some aspects of prison are not so good. For example, is it a good idea to mantain all prisoners together? In my opinion, prisoners needs some inspiring people to follow, not "in mates" that willl probably give them wrong ideas. Another point that can make people think that prison is useless is the time, if prisoners don't do activities they will get ideas, probably bad ideas. A full schedule can keep ther brain busy.
On the other hand, I think that prisons are a necessary evil, because we need some places to control and punish all the people that committed some serious offence.
In conclusion and my point of view prison are necessary but society can improve them a lot.