What!?
Do you even know where that "example" came from? It came from Schenck v. United States, 249 U.S. 47 (1919); this case was about upholding sedition laws for WWI which restricted political speech -- exactly the sort of speech the 1St Amendment was meant to protect -- protesting the war. (The case was wrongly decided, basically saying: the congress can do in war what it cannot do in peace.)
The whole "fire in a crowded theater"-argument is one that justifies that which is not justifiable: it is the expansion of "legal reading" of the Constitution to mean that which is not said. -- For you to use it only perpetuates the evil.
Do you disagree with that?
The rest of the Schenck case is not relevant to this particular concept set forth by the Court in Schenck, and I'd like to see any evidence you have that the founders intended for the 1st Amendment to protect speech without any limitations. I think any reasonable understanding of the 1st Amendment doesn't suggest that it, for example, would protect conspirators from prosecution since they were free to say whatever they wanted, or a bank robber since his statement "give me the money or else" would somehow be protected speech.