Jesus, I was talking about societies with modern justice systems focused on rehabilitation, not civil-war era wild west. Yes, of course absent a functioning justice system revenge cycles will occur. But the whole argument in this thread is about the relative merits of rehabilitation vs. punishment in modern society. And on that front the evidence on the outcome is pretty solid: Punishment-focused justice systems (like in the U.S.) result in more people in prison, are more costly and correlate with higher crime rates (not sure about the current evidence on causality, but I think it is pretty obvious that the trauma and stigma associated with a punishment-leaning justice system would tend to lead to more crime).

Studies quite consistently show that increasing the punishment for a given crime does not reduce the rate it is committed at, all other things being equal. Because guess what, criminals are either unaware that they are committing a crime/are committing a crime in a moment of passion (in which case the punishment is of no consequence) or they think that they won't be caught. Which is one of the many reasons the death penalty is so stupid. Catching criminals and bringing the to trial quickly is much more relevant than the severity of the punishment and the concept of rehabilitation is an extension of that: You find criminals quickly, you sentence them quickly and you invest in them leaving the justice system as quickly as possible to become productive members of society again. Why would I want to spend hundreds of thousands of Dollars on keeping someone behind bars for the rest of their life when I can also try spending a fraction of that on cognitive therapy, apprenticeships and social work to get them out of prison and into a stable life situation in which they have a decent chance of not committing a crime again?

It wouldn't be a problem if people would just stop advocating for going back to the bad old days. You don't know how it feels, but absolutely, if you lower the cost too much people are going to pay it.

The more we reduce this to some sort of transactional justice where everyone is supposed to pretend that nothing happened after a few years in a cage and everything is perfectly okay because people have "reformed" (never mind the people who keep going back...) the more you go back to the bad old days by making the justice system dysfunctional.

Also we can't very well make police more efficient because we don't really agree on the laws. Some people want all drugs to be legal (never mind the addicts who fall into a spiral where they rob others), some people want approximately no drugs to be legal (never mind the other costs). But there's yet to be any social consensus on whether we end up with the Tenderloin, Singapore or somewhere between.

Problem is that I think increasing leniency looks more or less like a phase change at some point. And nobody wants to acknowledge that historically, justice systems made society more peaceful via literal selection effects. Jail was not used so much in the past, there was more corporal punishment or death. Part of the problem is that jail only works while they're inside and imposes other costs, including moral ones.