I'll respond out of order: But a child rapist has no major impact on economic productivity, so... yeah, I'm starting to see the problem with this mercenary app

I'll respond out of order: But a child rapist has no major impact on economic productivity, so... yeah, I'm starting to see the problem with this mercenary approach to sentencing. This is almost trivial to account for, though, as long as you have a person looking at the numbers and making a decision - even if a judge sees that there's a large price tag if he sentences a child rapist, he's still going to do it, because the monetary value equivalent to "letting a child rapist back out into the world" is going to be ridiculously high, probably on the order of many millions of dollars. Same thing for other very serious crimes. Where it gets more interesting is cases like "college kid caught carrying eight pounds of marijuana", where there's no clear and present threat to anyone if the kid was given some sort of reduced sentence. If we can predict that, shouldn't we also be estimating the cost of the crimes they won't be committing? Sure, why not? In theory we lock people up because it helps society, right? So why wouldn't we want to consider all the possible higher order effects of different sentences on society as a whole? The problem is mainly that figuring out these effects can be very difficult, and I suspect that some of the second and third order effects end up being comparable in magnitude to the first order ones (direct cost of sentencing). Plus, in many cases we're really locking people up to satisfy a thirst for vengeance, not necessarily to help society in any way whatsoever. It would be nice if we had a better measure of what it actually costs us, though.