We actually don't. Obama tried to reduce the prison population by reducing the sentence or releaseing non-violent drug offenders. He found out that type make up less than 10% of the prison population.
The punitively long sentencing from the War on Drugs has meant that the people will go to great lengths to avoid arrest. Someone looking at 30-50 years for distribution won't think twice about murdering a witness if they think it will help them beat the charge.
Wait? What?
I'm from Wisconsin, and my second home is in Texas. In both places, non-violent drug offenders constitute the bulk of inmates by far. About 77000 of roughly 131000 inmates in Texas are in for drugs without theft or violent charges. If you factor out the ones in for big time distribution, it's about 62000 of the 131000.
https://www.texastribune.org/library/data/texas-prisons/crim...
Are you absolutely certain they said only 10% of people in prisons are drug offenders? In any case, at least where I'm from, drug offenders are, by far, the majority of the incarcerated.
EDIT: Hmm, it just occurred to me, are you only talking about Federal system prisons? Because most of our inmates are actually in the 50 state prison systems.
John Pfaff has done a lot of research into this [1], and drug offenders are a small minority (~20%) of prisoners. The bulk of prisoners are in for violent crimes, which makes the politics of decarceration... tricky.
[1]: https://ir.lawnet.fordham.edu/cgi/viewcontent.cgi?article=16...
And that's before couting the anti-deterrent effect you described.
John Pfaff, a professor who studies incarceration, found that despite a falling crime rate, the number of charged felonies has been holding steady. He suggests that aggressive prosecutors are charging felonies where previously they would have accepted a misdemeanor. He suggests that part of this is because they need to burnish their "tough on crime credentials", and part is the state generally pays for prisons and felonies where the county pays for jails and misdemeanors.
https://ir.lawnet.fordham.edu/cgi/viewcontent.cgi?article=16...
7 to 8 is as good as 10x.
Going from 1x to 8 is a huge 800% increase.
Whereas the correct 8 from the mentioned 10 is a mere 25% error...
In any case, the actual crime rates are about 3 times higher across the board. So we are incarcerating a lot more people for the same crimes somehow? About 2x as many. Alternatively, it's possible that drug crimes, which are an outlier, are pumping up our incarceration numbers vs some nations in the EU. Since they are not even arresting people for what we in the US would probably call possession at a minimum, obviously there would be no follow up prosecution and incarceration for those individuals? That might be the difference? But that's just speculation on my part. (It just kind of makes sense though, because we incarcerate a lot of people on drug charges. That's probably most of our prison population in some places.)
https://en.wikipedia.org/wiki/Comparison_of_United_States_in...
https://www.nationmaster.com/country-info/compare/European-U...