Dr. Jeffrey Miron at Harvard highlights two different approaches to libertarianism. The first approach, which he refers to as philosophical libertarianism, claims that individuals have rights. These libertarians believe that their rights are often infringed upon by government action, and therefore, are averse to most government action.
The second approach, which Miron spends the bulk of his time discussing, is referred to as cost-benefit libertarianism or consequential libertarianism. This approach attempts to analyze the whole set of effects of a particular policy. In this view, the net consequences of government action that actually occur in the real world are often negative.
Using the example of drug policy, Miron shows that, regardless of your personal views on rights, marijuana prohibition generates a large amount of negative consequences with little or no positive effects.