Ideally, lowering everything about the criminal system is a net good at all levels. Politicians and government are the ones who control expenditure levels along with what is defined as a crime.
Collectively, with would suit all levels of citizenry and government to raise threshold of what constitutes a "Crime", along with massive reduction of forces across all levels. However the first politician to 'defect' and recommend this gets lambasted as being "Weak On Crime". Unfortunately for the politician, it only takes a single person who was let out early and commit some assault/robbery/rape/murder to then show the 'evils and horribleness' of said politician.
Quote from the Slate Star Codex:
For example, ever-increasing prison terms are unfair to inmates and unfair to the society that has to pay for them. Politicans are unwilling to do anything about them because they don’t want to look “soft on crime”, and if a single inmate whom they helped release ever does anything bad (and statistically one of them will have to) it will be all over the airwaves as “Convict released by Congressman’s policies kills family of five, how can the Congressman even sleep at night let alone claim he deserves reelection?”. So even if decreasing prison populations would be good policy – and it is – it will be very difficult to implement.