Earlier quoted context omitted.
Cutthroats aren't a thing, and muggers are desperately impoverished. It's classism.
So you feel there's nothing wrong with placing non-violent criminals in with violent criminals?
Given what we know about prison guard misconduct and how countries like Norway handle their most violent offenders, I don't think it is the case that prison has to be terrible, violent, places. In every case I've ever heard of, compassion and rehabilitation for criminals of all types is the best way to reduce recidivism. Punishment turns out to not be that much of a deterrent for desperate people who think they screwed either way.
And given that minimum security federal penitentiaries have the nickname "Club Fed", it would seem that they don't serve as a very significant deterrent.
The full, correct answer is that the entire prison industrial complex needs to be torn down and rebuilt. Unfortunately, there is too much money in it for that to happen anytime soon in America.