"Any such view will require that you specify the 'good' whose protection or emergence will be promoted by a regime of free speech; but once such a good has been specified—be it the discovery of truth, or the realization of individual cognitive potential, or the facilitation of democratic process (the three most popular candidates put forward in the literature)—it becomes possible to argue that a particular form of speech, rather than contributing to the realization, will undermine and subvert it. This is so because in a consequentialist argument freedom of speech is not identical with the good but is in the service of the good; it is not a prime but a subordinate value, and when its claims conflict with those of its superior, it must give way. What this means is that insofar as you hold to a consequentialist view of free speech—insofar as you have an answer to the question 'What is free speech for?'—you are already committed to finding in a particular situation that speech with certain undesirable effects should not be tolerated; and what that means in turn is that there is no such thing as free speech[....]"1What about the first option of valuing free speech for its own sake? Fish acknowledges this as a logical possibility, but claims free speech defenders in practice always end up appealing to the instrumental view. If so, then there wasn't much reason for John Durham Peters to write a whole book criticizing modern liberals for valuing free speech for its own sake.
Fish's point is that "free speech" is a lofty and pure-sounding concept, but implementations of free speech always exclude categories of speech. We see this in the way the First Amendment to the U.S. Constitution mentions no exceptions, yet legal practice involves a complicated mess of exceptions. Free speech is a label that political victors get to apply to the mix of free and non-free speech they prefer. Fish isn't offering his own "pure" theory of free speech. Rather, he wants readers to realize that every free speech brand is a mongrel.
1. Fish, S. (1994). There's no such thing as free speech: and it's a good thing too. New York, NY: Oxford University Press. p. 13