Boycotts are particularly unattractive when intended to squelch speech. In each of the previous examples, boycotts were organized to harm the target economically so that the target would pressure the original speaker to, well, shut up. The power of ideas is abandoned for the power of economic coercion.First of all, call screeners act as censors of free speech and almost every rightwing radio gasbag has a call screener. Second, should a well-informed caller somehow get through and begin an actual debate with the host, they are dismissed as "seminar callers" who are not to be taken seriously. (I believe Fats Limbaugh coined the term) Third, in many cases, the show isn't aired live so a radio listener doesn't have the chance to respond at the time.
The op-ed asserts without any evidence that "secondary boycotts have long been recognized as harmful to civil society. They rend the social fabric by making it difficult for people to simply live their lives." I guess this clown doesn't listen to the harangues and lies of Limbaugh, Hannity, Beck, Levin and many others because they all encourage their listeners to "piss off a liberal."
You might want to join the conversation on this Volokh Conspiracy post.