Imprisonment is the archetypal restriction on liberty, the paradigm case . Liberty is such an important constituent of individuals' lives that we need exceedingly powerful reasons to throw people in prisons, even if all they did was restrict liberty, like the village in the TV series The Prisoner . But it's increasingly obvious that prisoners are not just unfree, but systematically brutalised in the most shocking ways, as illustrated in this barnstorming call to arms from Christopher Glazek in nplusone magazine :
America’s prison system is a moral catastrophe. The eerie sense of security that prevails on the streets of lower Manhattan obscures, and depends upon, a system of state-sponsored suffering as vicious and widespread as any in human history. Dismantling the system of American gulags, and holding accountable those responsible for their operation, presents the most urgent humanitarian imperative of our time.
The numbers, on prison rape particularly, are truly disturbing:
In January, prodded in part by outrage over a series of articles in the New York Review of Books, the Justice Department finally released an estimate of the prevalence of sexual abuse in penitentiaries. The reliance on filed complaints appeared to understate the problem. For 2008, for example, the government had previously tallied 935 confirmed instances of sexual abuse. After asking around, and performing some calculations, the Justice Department came up with a new number: 216,000. That’s 216,000 victims, not instances. These victims are often assaulted multiple times over the course of the year. The Justice Department now seems to be saying that prison rape accounted for the majority of all rapes committed in the US in 2008, likely making the United States the first country in the history of the world to count more rapes for men than for women.
It is a radical piece, arguing for the complete abolition of prisons:
If, in the popular imagination, the primary purpose of prisons is to keep us safe from (the vanishingly small number of) people like Charles Manson, then we should simply kill Charles Manson. Prison abolitionists should be ready to advocate a massive expansion of the death penalty if that’s what it takes to move the discussion forward. A prisonless society where murderers were systematically executed and rapists were automatically castrated wouldn’t be the most humane society imaginable, but it would be light-years ahead of the status quo. (Interestingly, unlike rape, homicide has one of the lowest recidivism rates of any crime—you can only murder your wife once—suggesting that death row inmates may pose less of a security risk than other categories of offenders.)
Obviously his article is focused on the USA, and uses US statistics—typically the UK system is seen as far less brutal, perhaps because we do not have the deep-seated racial angle seen in the US, and/or because our drug laws are enforced in a slightly less draconian manner. Having said that, according to the Howard League for Penal Reform's new Commission on Sex in Prison  the data isn't widely available to make that sort of judgement.
But even if the UK is much better than the US, and even if we don't want to go the whole way to abolishing prisons, the matter is clearly of huge significance, but at the same time bizarrely underreported by most sources, despite the fact that around the world millions of people are in prison (e.g. in the USA, the prison population is bigger than any city except New York, Los Angeles or Chicago). Surely there must be a better way to deal with crime than forcing 15-year old petty thieves together with violent gangs who repeatedly rape them until they kill themselves?