Well --- like I said --- I'm all for having 3 levels --- put the bad check writers and pot smokers together in one prison, the moderately violent who get into an occasional fist fight together in another, and the killers, rapists, and child abusers together in another.
That makes sense from a security standpoint; then you can keep a better watch on the killers/rapists/child abusers. Still, if guards see bad stuff going on they should stop it. Not that anyone can stop what is a natural known consequence of bad behavior. Like, if some rapes my wife or daughters, and I catch them before anyone else does, a natural consequence might be me clubbing them about 10 times in the head, tying them up and pouring boiling water over their b&lls. In prison, a natural consequence of rape, is in turn being raped by someone (with or without soap).
But again, we need to follow our laws as well as we can, and states shouldn't habitually and deliberately ignore these sorts of things in prisons.
That proposal was put to the warden of San Quentin prison in California a few years back, and his reply was that unless the non-violent types were mingled in with the violent types the prison would be totally unmanageable (probably due to ACLU lawsuits limiting their ability to take appropriate action to deal with violent prisoners). California does have Pelican Bay, where they send the truly unmanageable prisoners, and the Security Housing Unit there is used for solitary confinement of the true predators. And I think the ACLU practically has a branch office there.
California's big problem is neutralizing gang violence - and I think, unfortunately, that gangs have infiltrated both the prison population and their guards. Judging by the news stories we've seen lately, on wonders whether the state or the Crips are really running the prison system.
The best solution is to humanely euthanize violent predators - preferably with a .45 - produced by their intended victims at the scene of the crime. ;)