Convince me: Prison is for punishment not rehabilitation

What should the main purpose of prison be?

Is it to punish criminals in order to provide justice for those harmed by them which may have the side effect of deterring them from offending again.


Is the purpose of prison to help the criminals and rehabilitate them so that they are less of a threat to society when they come out?

Convince me that prisons are primarily for punishment.

Exercise your brain.