Yeah the conclusion from here [1] is that the biggest reason a prison can reduce crime is not because of rehabilitation or deterrence (even in places that try to do either) but because of incapacitation. It holds people in their prime age of doing crime (15-30) and spits them back out when they're too old to do those anymore. The obvious conclusion is that exile will have the same effect, but we don't have place to exile people to anymore.

1. https://www.astralcodexten.com/p/prison-and-crime-much-more-...

Moon and Mars are coming soon.