In a conversation with Russ Roberts, Becky Pettit says
educational inequality has become so dramatic that among young black men who have dropped out of high school, a huge fraction of them, upwards of 2/3, can expect to spend at least a year in prison
She says that much of the increased incarceration in recent years is for drug offenses and nonviolent property offenses. To a libertarian, thinking along the freedom-coercion axis, it is drug prohibition itself that is offensive. Any time the government declares a “war” on anything, libertarians assume the worst. And they see drug use as a choice with which the government has no right to interfere.
Progressives have wanted to see drug users as oppressed, the victims of a bad environment and of “pushers.” Progressives see no problem in having government act to protect individuals from their bad impulses, in this case the impulse to take drugs. However, when it comes to punishment and incarceration, progressives would want to exempt users and focus on drug sellers. For progressives the idea of punishing those who profit from selling drugs has some merit (I could be uncharitable and say that for progressives the idea of punishing those who profit from anything has some merit).
To conservatives, both drug users and drug sellers are on the side of barbarism. Along the civilization-barbarism axis, the high incarceration rate among those involved in the drug trade probably looks more like a feature than a bug.
In this case, I find the libertarian freedom-coercion axis so compelling that I have difficulty seeing any merit in looking at the issue from the point of view of either of the other two axes. Perhaps I am not being sufficiently charitable. Along these lines, see the op-ed by Gary Becker and Kevin Murphy.