> If penalties for mugging/robberies were lowered to pick pocketing levels, Paris would have muggers in every train and far fewer pickpockets.
This is a good point!
But I think this effect is less about the "incapacitation" issue discussed above (i.e. we would have muggers on every train because we wouldn't have detained the muggers for long enough), and more about deterrence (i.e. we would have muggers on every train because pickpockets would lose a disincentive from mugging).
There are multiple dimensions to picking how societies respond to crimes:
- denunciation: we publicly send the signal that your behavior was bad
- retribution: we want you to suffer
- rehabilitation: we want to help you become a better citizen
- incapacitation: we want to stop you from committing crime
- deterrence: we want other people to be afraid to commit crimes
- ...
And all of these carry different associated values. My suspicion is that when people attempt to justify the prison system based purely on the incapacitation effect, they're trying to don some faultless, sterile, harmless guise. "I'm not a bad guy for wanting people to be in prison; I just want my neighborhood to be safe!" But I think often a desire for denunciation, or retribution, or even angst about deterrence is at play.