I would submit that such statistics look more appalling (from a US perspective) than they really are. Note that a number of places with a 'low' or 'lower' percentage of their population being incarcerated are also places where other forms of what we term violence here (e.g. honor killings, tribal war, genocide, etc...) are more frequent or commonplace or the police system in general is lacking. Not all, mind you, but some of locations in South Africa, the Middle East, and Asia, for instance. Some of these places are also home to "camps" and are harder on their prisoners &/or have harsher conditions than we here in the US. In some respects, this goes back to my thought about people not fearing prison here as much as in the past.
Getting back to reducing the prison population, I agree that some in prison don't need to be (just as much as some not in prison should be). For those advocating legalization of certain substances which are currently illegal, what would be your proposed way of legalization while not inducing new opportunities for incarceration (e.g. follow the approach taken by the Netherlands)? What about capital punishment for repeat, violent offenders?
Regarding the comment about closing half, which I'm sure was not meant to be exact, of the military bases around the world, I would agree that there are likely some could be closed, but I would disagree a large # should be for the sake of cutting costs. Where does one draw the line between saving money and having strategic positioning?
Personally, the best way to reduce spending starts on the Hill (obviously) w/ the lobbyists and pork barrels for our elected officials. Cost plus programs are not as rampant as before but still exist and for FFP programs/contracts, there is not much more than wrist slapping, if anything, for those w/ the better lobbyists or larger campaign contributions when spending if overrun, if not steamrolled.