One of the great difficulties of consistent libertarianism is that of making people bear the full consequences of their own actions and choices. Another great difficulty, indeed, is whether we should much care to live in a society that found a way of doing so.
“You must be the best judge of your own happiness.”
Jane Austen said that, in Emma, but the statement is also a keystone principle of modern microeconomic theory, and it provides the epistemic foundation that makes benefit-cost analysis possible. The only way to know people’s preferences is observe the choices that they themselves freely make; all inferences about the “public” interest must begin there.