> But those people aren't innocent.
Some of them certainly are; we get “beyond a reasonable doubt” wrong often enough with murder that there are fairly regularly news articles about exonerations after lots of resources from public interest groups dug out the truth.
Just because no one is spending the same resources—and even if they were no one would treat the results as newsworthy—on lesser offeses doesn't mean people aren't imprisoned wrongly for them (perhaps far more often, largely on plea deals, then is the cases for wrongful murder cobvictions.)
> But again, I think this flows more into the "mass incarceration" problem/rate than it does into the "imprisoning innocents" problem/rate.
Mass incarceration is a product of mass criminalization plus high imprisonment penalties on the books. That also produces a volume of criminal cases too high to handle without expedited process, and a heavy pressure tool in terms of high potential penalties that can be traded far down for guilty pleas. With many of the accused unable to afford more than the barest defense, that also creates a huge likelihood of significant imprisonment of the factually innocent on top of that which comes more directly from mass imprisonment plus the failure rate of even ideal criminal process.
That is, mass incarceration causes, rather than being a separate unrelated problem from, imprisonment of innocents.