Were I to rewrite the position on the cruelty of solitary confinement from a Marxist historical-materialist perspective (rather than phenomenological), this is what I would say:
Consider the recent article on the social and habitat isolation of the bipolar Colorado mass murderer James Holmes.
Prolonged isolation inflicts a harm, one that can never be justified. This harm is ontological; it dismantles the very structure of our relational being–our species being as a social species, how our senses are built to depend on communicating with other humans. Consider a basic example: Every time someone walks around the table rather than through it, or bumps into a table, my brain quickly mirrors their action and receives an unspoken, usually unremarkable, confirmation of my own experience that the table exists in a specific way in the world, and that my sensory experience of tables is shared by others.
When I don’t receive such implicit social information, I can usually ask someone — but for the most part, we don’t need to ask because our sensations and concepts are already interwoven with the sensations and concepts of many other sensing, communicating beings who relate to the same world from their own unique perspective. This multiplicity of shared perspectives within one world is like an invisible scaffolding that helps order, prioritize, provide boundaries to, and confirm my sensory experience of the world.
If we truly want our prisons to rehabilitate and transform criminal offenders, then we must put them in a situation where they have a chance and an obligation to explain themselves to the others we need them to be accountable to, to repair damaged networks of mutual support, and to lend their own sensations and unique perspective to communities creating both shared meaning and the world beneath and informing meaning.
Consider as well that some people’s epistemologies-ontologies are more robust under torture, as Elaine Scarry famously discussed–In particular, those that recognize human intercourse in terms of “making” and “unmaking.” People whose epistemology-ontology allows them to recognize that someone is trying to unmake their world, for example via solitary confinement torture or other forms of torture that are designed to alienate your bodily senses from you, to unmake your world and impose theirs upon the vacuum that they have created in you– people with such making/unmaking perspectives are more protected from torture, from imperial, colonizing unmaking.
That doesn’t mean it’s easier, knowing that someone is laboring to destroy your world in order to implant their order within you. And being able to resist might mean the prisoner is tortured to death. Torture is to be abjected as an abomination against our social humanity.