Whether or not the purpose of jail and prison is to reform inmates or prevent them from interacting with other people is not the basis of my ideas. The same logic applies to whether or not inmates are deserving of compassion.
The basis of my ideas is the most literal and rudimentary purpose of jail and prison: involuntary confinement to prevent defendants awaiting trial from fleeing or committing further criminal acts if they're guilty and punishment for criminal behavior - and nothing else. This entails eliminating other forms of punishment, namely abuse from other inmates, and the only way to do so is to isolate prisoners to an extreme degree.
Penalization is to be carried out by the state - not by fellow inmates. A jail or prison in which inmates can prey on one another is one over which the state does not have complete control, which is unacceptable.
Solitary confinement is itself a punishment against the prisoner, above and beyond removing them from society and placing them in a separate living space.
I think the ideal for any grievance would be for the two parties to resolve between themselves without involving the government or the court. Everyone buries the hatchet and everyone lives in peaceful bliss. The only reason why we have courts and prisons in the first place is because citizens do not live in peaceful bliss. They act out against one another and will never willingly make amends for the things they do unless it is imposed upon them.
The main reason why we entertain the concept of "humane prison treatment" at all is because of religious sentiments. From a naturalistic standpoint, the prisoner is a disfunctional organ of the society and must be quarantined with the other infections to prevent further damage and spreading into the healthy tissue. There is no regard for the infection, only for the healthy tissue. This is how criminals have been treated and viewed for most of human history, in almost all human cultures. It is only relatively recently that we have considered the rights and condition of the prisoner as something worth caring about.
Solitary confinement might protect them from potential gang violence, but let's just take it a step further: confine all prisoners along hallways, shackled to the walls, unable to reach one another. That solves the problem of solitary confinement destroying their psyche, but also solves the problem of prisoners attacking one another.
What do you think?
Most modern countries inherited their prison mentality from the slave trade. We learned the logistics of herding and trapping other humans because we've been doing it for 1000s of years.