Cops can stop you without any reason for suspicion and aren’t forthright about your rights. Their general militarization and lots of stories we read about cops give us reason to fear them. But are libertarians right to be mad to be this angry about it?
They point to the Fourth Amendment and may have a decent case there based on certain interpretations of the Constitution. But originalists can’t make this claim because the Founders had no intention of the Fourth Amendment applying to state and local governments.
The greater problem is that the usual libertarian normative belief about roads is that they should be privatized. Why should the government provide a good the private sector could? If the market did not build enough in the way of roads, people could be given vouchers and then pick which roads to use.
And if roads were privatized surely the road companies or our auto-insurance companies would pay for police or some other way to enforce safe driving. Maybe they would do this more efficiently than the government. But it is hard to imagine private roads would exist in such a way that those who had done nothing wrong would never be monitored. Insurance companies might want to put trackers in our cars that could tell if we were speeding or swerving between bar parking lots, for example.
If DUI checkpoints were found to be inefficient they would stop— but they won't, because people have an interest in preventing drunk driving. That we let Facebook and Google know everything about us reinforces the point that operating through the free market doesn't mean we don't give up some of our rights to privacy.
Given what we’re learning about the NSA privacy is rightfully on top of all our minds. But DUI checkpoints aren’t the issue to get angry about. And those promoting liberty should be explicit about their values.