If you can't option for stateless expatriation & deportation & outlawing (within borders) & and re-entry ban, in lieu of years/decades/life in prison, then what

If you can't option for stateless expatriation & deportation & outlawing (within borders) & and re-entry ban, in lieu of years/decades/life in prison, then what is prison actually for? Certainly not human rights respecting public safety. Only reason I can see is it's sanctioned hunting and torture (through humiliation and deprivation) of a very vulnerable class by the state: criminals. ... Maybe substitute outlawing for imprisonment generally, and offer imprisonment as the rehabilitation option which protects the guilty from the victims' retributions. If pedo hunters are an example, I'm sure there are lots of grown up school bullies who'll go around making outlaw lives hell out of pure joy alone.