In Arizona, you can use force to prevent the commission of a crime. If the demonstrators are engaging in criminal behavior, such as jaywalking, I suppose you could be justified in the use of force to prevent that crime, e.g. not downshifting.
Of course, if you reasonably believe that the demonstrators are about to cause you or another serious bodily injury or death, then you are justified in using deadly force to prevent that from happening.
These aren't necessarily areas of the law where I would suggest experimenting, though.
In addition to NEW's comments, certain content-based restrictions are perfectly legal, as some expressions are not at all protected by the First Amendment. For instance, "obscenity" is not protected speech, and speech that incites people to immediate violence is not protected, either. Of course, no one has a good nickle definition of "obscenity". Its definition is couched in words such as "patently offensive", "lacking serious literary, artistic, political, or scientific value," and "appealing to the prurient interest," all of which are measured according to a hypothetical "community standard."