Democratic Senator Dick Durbin accidentally made the libertarian case against the drug war and prison privatization when two of his tweets were juxtaposed against each other:

And this one:

When placed next to one another, it seems as though Durbin is admitting that drug and prison policies are driven by fiscal incentives instead of what they should be driven by - protecting the community.

Many Libertarians argue against the Drug War, saying it's spent billions and has not significantly lowered drug use, or lowered illegal drug transactions. While they're usually for privatization of government functions, many also criticize how private prisons are becoming a funding stream for governments - they say this creates an monetary incentive for the law enforcement to imprison more and more people.

I don't necessarily agree with these arguments - crime has dropped precipitously over the last decades, and I think that's due at least in part to more and better policing. That also doesn't mean that we can't have humane conditions for prisoners, or that we should not review prison sentencing guidelines to make sure they're effective.