As a deterrent to lawbreaking we should return to public executions for all appropriate crimes.
This should include the death penalty for treasonous actions, which seems to no longer even be punished at all let alone by its original penalty.
Just as crime levels rise when the law is not enforced, so to major crimes deserving of the death penalty also increase when there is little public visibility.
Seeing another humans life end as a just act of the state for appropriate crimes will in fact deter some from committing like crimes.