> Every free speech "purist" I've ever met limits
  > their opinion of control to the government.

There are people that have argued for free speech outside of this narrow lense. John Stuart Mill, one of the original advocates of free speech, argued against censorship by private parties.

He discussed the "the moral coercion of public opinion" and wrote that "the chief mischief of the legal penalties is that they strengthen the social stigma" and added that "It is that stigma which is really effective".