We hear again and again that "over-incarceration" or "incarceration nation" is the subject of considerable public angst, and that there is a "growing, bi-partisan consensus" (see, e.g., here) that we should scale back the prison population ("prison population" being the euphemism for "adjudicated criminals whose offenses are serious enough to earn them a prison term").
Is that proposition true? Is the public up in arms in any sense about "over-incarceration"?
No, it is not true. Indeed, the subject barely makes the radar screen, according to this quite informative Washington Post article. Subjects of more concern to the public are: Education, budget, healthcare, taxes, transportation, infrastructure, marijuana, energy, jobs, pensions, crime, and ethics. Only after that is prison (which managed to get mentioned as the third-ranking concern in a total of six states), followed by labor, environment, elections, housing, immigration, civil rights, the economy, guns, privacy and a scattering of others.
So called "over-incarceration" may well be an obsession with the academic left, dead-end liberals and, naturally, criminals, but the public that pays the bill (1) is all but indifferent, and (2) guess what! -- cares more about crime.

Over incarceration is the "global cooling,warming,climate change" of the criminal justice left.
As we have seen, some will even fake being libertarian to get attention from anyone not on the kooky left fringe.
It's not working.
Yes, on some shallow and generic level people want fewer people in prison and will showcase that compassion in a poll or survey. It's not cool to want to keep supposed "low level" offenders in prison just like it is not cool to want to destroy the earth. However, we also know that they enjoy low crime rates and less risk to their families. When the rubber hits the road in the real world, they rightly want to keep bad people behind bars.
Bill, my read of the WaPo piece is that crime and prisons got equal mentions in the "top 5" with each getting mentioned by reporters as a "top 5" issue in six states. Moreover, the frequent mention of "budget" as a concern can (and should perhaps) be viewed as a concern that relates to the high costs of state prison spending relative to other possible state crime-control efforts.
Also this data concerns what reporters are saying state legislators are concerned with, and thus this is a thrice-removed gauge of what is a public concern --- an impressionistic metric of what reporters think legislators thiink is most important (which, in turn, likely is at best an imperfect proxy for what the public thinks is important).
Most fundamentally, nobody I know seriously disputes that the public cares about crime, but also nobody I know seriously questions whether the public is eager for taxpayer expenditures to produce the most public benefit/dollar. And it is not just folks on the left, but lots of self-described conservatives now questioning US investment in costly use of lots of prisons --- folks like Grover Norquist and Erik Erickson and Rick Perry and Ken Cunchinelli and other "Right on Crime" signatories who believe, as I do, that government programming should always "be evaluated on whether they produce the best possible results at the lowest possible cost, but too often this lens of accountability has not focused as much on public safety policies as other areas of government."
TarlsQtr is 100% right that the public wants to keep bad people behind bars, but recent votes in many states shows the public no longer views marijuana dealers as "bad people." And, notably, as these matters have come to a vote in California in the last two elections --- via 3-strikes reform in 2012 and Prop 47 in 2014 --- a majority of the public who voted did in fact vote to decarcerate some "bad people."
I respect your (accurate) refrain, Bill, that the general public is not as concerned with prison populations as is the academic left. But that same point could be (and often is) made on a host of other flash-point issues ranging from gun control to climate change to abortion access to health care reform to same sex marriage. And, critically as we look over these historically divisive issues, there now does seem to be a lot more folks on the right who agree in the prison context with what the folks on the left are saying than in any other area I just listed.