I didn’t say people shouldn’t be in prison, all I am saying is that jail time does not dissuade criminals from breaking the law. As you know, our penitentiaries are overflowing, but crime rates aren’t going down.
I think a broader view might be better served for some "crimes" in this discussion. Auto theft in WI has sky-rocketed in my state since the DA in charge (Milwaukee County) intentionally decided not to prosecute auto theft. Prior to penalties not being handed down, auto theft was typical in Milwaukee to other cities of similar size. Now we lead the nation (per-capita). The thieves openly admit that they do it because they won't be arrested, charged or penalized in any way, if they ever get caught. 12 & 13 year-olds are now stealing cars with abandon. They have actually become semi-famous on youtube as the "Kia-Boys".
Murder, OTOH, probably falls more closely into your intended position regarding penalty as a deterrent....not so much. But every crime is different...
So does jail-time act as a deterrent? Sometimes yes, sometimes no....nothing is ever black and white...but in the case of auto-theft, it clearly does deter crime (in my locale).
And our prisons have been above capacity for many, many years...the data is available online quite easily. So that means we either need more jails or a different "effective" method of rehabilitation....which has yet to be discovered.
All of the above rambling doesn't even touch upon a crook, not in jail as he/she should be, out and free to commit crime, as in Darryl Brooks. He should have been incarcerated (in 3 states), but was out on intentionally-low bail. He never should have been ABLE to kill 7 people and injure 63 more last Christmas. He should have been locked up. This concept is not the deterrence to crime as ya'll were discussing, but it is a relevant issue, none-the-less.