Could you tell me how 'trial by public opinion' in this case is different than a call for a boycott or picketing? That is, I assume that you think people should have a right to boycott and picket. Those are well protected free speech rights in the US.
McCarthyism and the blacklist involved decades of government pressure, including passing various laws against Communists at both state and national levels. The blacklist specifically started after various people were cited for contempt of Congress for refusing to testify to the House Committee on Un-American Activities.
That's hardly the same as a few organizations calling for a boycott of Firefox and a few people threatening to quit their jobs at or stop volunteering for Mozilla, is it?
As much as I strongly disagree with the Prop 8 folks, I think resorting to trying them in the court of public opinion is fundamentally wrong.