Falsely yelling "fire" in a crowded theater is an example of speech that is not protected by the First Amendment to the US Constitution. You can be wrong in America, but if by being wrong, you also cause great harm ... this is something you have no right to do. But I wonder, if you whisper in some one's ear (someone you know is unstable) and influence them to yell "fire," even though they know it is not, is your whisper protected? What if your influence is much louder than a whisper, but a broadcast that goes into the homes of millions? Some of those homes have extremely unstable individuals in them. We, Americans, also live in a society where we have ready access to guns. Is that speech protected? I think the problem is causality. You can prove that the yelling of "fire" caused the crowd to trample themselves, but you cannot prove causality that a Fox News broadcast caused an act of violence.
I hear this metaphor in free speech arguments several times a year. It actually originates from Oliver Wendell Holmes Jr. in a 1919 Supreme Court case called Schenck v. United States. In this case, the US Supreme Court ruled unanimously in favor of restricting Charles Schenck, the Secretary of the Socialist Party, from passing out fliers against World War I. The harm in this case was the military's ability to recruit. This amazed me when I read this today. I cannot imagine Congress trying to pass a law now preventing us from passing out fliers against the war. It just seemed so wrong to me. This is because in 1969, the Schenck v. United States was overthrown by Brandenburg v. Ohio. The definition of harm in the original case was further defined to mean "imminent unlawful action" aka a riot. So you cannot incite a riot, but you can pass out fliers against a war or even use ethnic slurs. What an awesome country! Since I am wrong just about everyday, I am grateful that my right to be wrong is protected. It is just so infuriating some days when some are so very wrong and there is nothing we can do about it.