Ezra's got a pair of posts about prison rape that I recommend. It's an important issue, with lots of different angles; male prisoners are more likely to be raped by other prisoners, whereas female prisoners are more likely to be raped by male guards—but, in either case, rape (or the constant threat of rape) is an unspoken sentence rendered upon almost anyone who is convicted to spend time in an American prison.
It's interesting, by the way, to see how different the comments threads are from typical rape threads. No one is suggesting that rape victims in prison are "crying rape" for ulterior motives, for example.
Also, although no one is saying, "Hey—if people don't want to get raped, they shouldn't commit crimes for which they'll be sent to prison if convicted," unfortunately its absence isn't because that sort of victim-blaming isn't operative, but, instead, boasts such wide tacit agreement that it isn't even worth saying. There are plenty of people (including progressives) who simply don't blanch at the thought that rape is a likely part of any prison sentence.
I've heard that attitude ascribed to many things, from ignorance of the prevalence of prison rape to contempt for the rule of law, but I suspect the predominant quality which most closely tracks with holding the position is never having been raped oneself.