Freedom of expression, as a philosophical problem, is an instance of a more general problem about the nature and status of rights. Rights purport to place limits on what individuals or the state may do, and the sacrifices they entail are in some cases significant. Thus, for example, freedom of expression becomes controversial when expression appears to threaten important individual interests in a case like the Skokie affair, or to threaten some important national interest such as the ability to raise an army. The general problem is, if rights place limits on what can be done even for good reasons, what is the justification for these limits?
A second philosophical problem is how we decide what these limits are. Rights appear to be something we can reason about, and this reasoning process does not appear to be merely a calculation of consequences. In many cases, we seem to decide whether a given policy infringes freedom of expression simply by consulting our conception of what this right entails. And while there are areas of controversy, there is a wide range of cases in which we all seem to arrive at the same answer. But I doubt that any of us could write out a brief, noncircular definition of freedom of expression whose mechanical application to these clear cases would yield the answers on which we all agree. In what, then, does our agreement consist?