I'm entirely receptive to the idea that we're incarcerating far too many people, but I think that preserving a relatively low prisoner-to-guard ratio is a good idea.  Having more guards creates disincentives for prisoners to attack them, and having more guards available means it's easier to subdue someone without using lethal force.  The Bureau of Prisons and the American Federation of Government Employees are currently negotiating over whether to provide all prison guards in the federal system with custom-fitted stab-resistant vests and non-lethal weapons like pepper spray and tasers.  I'm not really sure about the wisdom of the latter, but it does seem like helping prison guards feel that, even if they're attacked, they're likely to survive, is probably a good thing.