Anecdote; as a teenager, my brother started to stray. He was caught by the law. The consequences were light, but (speaking as a bystander) I think the fear of the experience itself- being arrested, booked, and charged- served as a form of punishment, and as best I have been able to tell pretty much straightened him back out.
Of course, he is a fundamentally gentle soul; this anecdote doesn't apply to the hardened criminals.
single digit percentages of a given population being deterred is not something to be taken lightly; a penal aspect is both an extant and an historical imperative.
Of course, he is a fundamentally gentle soul; this anecdote doesn't apply to the hardened criminals.