And so am I. I feel the current prison system does little to rehabilitate convicts. I also feel that many sentences are extremely lenient in terms of length.
I didn't say that poverty alone makes people into criminals. It is a combination of a variety of factors which can contribute towards people turning to crime. For the overwhelming majority of people convicted for violent crime - and this is a fact now, not an opinion - the individuals responsible did not suddenly go from being ordinary people from ordinary backgrounds to being killers. There is almost always a long trail of abuse and deprivation which leads to it. This is an indisputable fact, demonstrated by countless studies. And I am not using this to excuse their behaviour, but rather to explain the context in which their attitudes towards others have developed. A child who grows up in a violent environment is far more likely to believe that violence solves problems than a child who grows up in a normal environment. Combine that with emotional problems from broken families, abusive parents, poverty, poor education (many violent criminals have low IQs) and other social problems and you have an explosive recipe for problematic people. Look at countries that have higher standards of living and less deprivation; you'll always find they have lower rates of violent crime too.
Treating people as if they're subhuman is likely to reinforce their behaviour though. In much the same way as a dog who is treated cruelly by its owner is likely to become vicious and attack others, a huge part of the criminal mindset is insecurity and the problems that come with that; if you continue to treat the person poorly, you'll reinforce the feelings of inadequacy and resentment which will likely make the behaviour even worse. Why do you think so many criminals have such a high rate of re-offending? The solution to most criminals isn't to lock them away in a dank dungeon, depriving them of their human rights and feeding them scraps of bread and water; on the contrary it's a matter of educating them, and putting them to work so that they can form a productive identity in which they have a role to fulfill in society.
Of course I am aware that this isn't a magical solution that will work for everyone, but I'm very much in favour of making prisons a productive place where inmates are not only provided with skills and discipline, but are also put to work to pay for their room and board. As an example, some American prisons have been very successful in cultivating their own crops which keep costs down and gives the inmates something to do. This in turn reduces violence within the prison itself, gives the prisoners a sense of purpose by keeping them busy, and teaches them skills they can actually use when they are released, which reduces the number of potential re-offenders.