not true, even in feudal times there were less crimes because of harsher punishments, even in much harder times, i don't think that prisoners should be abused by the way while in jail also (and this happens mostly by other prisoners as well) that should be strictly prohibited
Sounds like you're pulling stuff from out of your ass, the truth here is corrective vs punitive, corrective leads to a lot less recidivism, unlike punitive. All you have to look at is recidivism rates in the US vs northern European countries that have corrective prison systems in place. Norway has a 20% recidivism rate compared to the US's 67.8% withing 3 years, and 76.6% within 5 years.
Societies that confuse prison with vengeance have more crime, and end up worse for victims themselves.