I'm not sure that system would work here, as with the way things are now, we might lose a third of the population.
But then...come to think of it...that might not be so bad.
Please do not think that that horrible movie had anything in common with the book (aside from names and some generalities).I highly recommend the book.
It's a reversion to the old system. Prisons are a relatively modern invention. Older societies could not afford to feed large numbers of unproductive men. If somebody demonstrated that he was too dangerous to continue to live in the society, the only real choices were exile or execution.