And bring back exile. Countries used to forcibly eject citizens who committed certain crimes.
Why lock them in a small room for decades? If another country is willing to take them, send them there.
If not, far cheaper to set up a prison colony like Australia or Georgia and far, far more humane.
Our prison system is an abomination indeed.
I spent only a few hours in jail once and learned all kinds of illegal things, where to find the local prostitutes, who to see about illegal drugs, etc. Prison is not a deterrant but a form of coporeal punishment.
Exile may work for some. But like the expulsion of MS-13 to Latin America. They now dominate huge sections of El Salvador and have now come back to the USA:
MS-13 - Infogalactic: the planetary knowledge core
So for gang bangers its better that they either leave permanently their gangs or they are executed after a Death Sentence. Hades in that sense is the most secure prison before their appearance at the Great White Throne Judgment.