Paying your debt to society part 1

I could never understand how going to prison is called paying your debt to society.  How does costing society more paying a debt?  If I borrow money from a bank they wont give me a place to stay and three meals a day for five years then say it is clear so why do we do that for criminals?  Many people work two jobs in undesirable conditions to have a place to stay and three meals a day.  As of 2005, there are 2 million people locked up in federal, state, and county facilities. At a cost to tax payers of $32 billion each year.  Much of this is state and local money but if this expense was eliminated the states wouldn't need federal funds.  My solution is make criminals do like the rest of us work or die.  I will talk about the death side first.  Last year UFC made an estimated $200 million and it is an emerging sport.  This gave me an idea why not have criminals do what they are good at killing.  If each criminal was given the choice to fight in death matches and just 5% took it that is 100,000 fighters.  That 5% would save $1.6 billion plus at least $200 million in income.  That's not bad $1.8 billion by offering criminals a new option.  In my next post I will talk of how to run it.