It’s not really possible to measure this over the long run. Short and medium term studies show that mass incarceration dramatically reduced crime in the US, mostly by literally removing violent young men from society, but that’s not the main reason why I support strong punishment. The moral decay of a society can take a hundred years to set in, but once the consequences become apparent, it can be too late to do anything about it. There is a lot of wisdom encoded in the ways of the past. Retribution for crimes is a universal institution for a reason.