That's the equivalent of putting somebody in solitary confinement for life, which does more mental harm than good, we already have plenty of scientific evidence

That's the equivalent of putting somebody in solitary confinement for life, which does more mental harm than good, we already have plenty of scientific evidence for this not just for Humans but many other social animal species. Pigs for example tend to be very clean and smart animals, that is until you hoard too many of them in too little room, then they start to act nasty towards each other because of the stress that situation represents to them. The behavior you are describing also has little to nothing to do with psychopathy, which is far more prevalent outside of mental institutions and prisons than most people would like to admit.