A freedom to do something is no protection from social enforcement of the consequences of you exercising that freedom.
Ridiculous. By that argument, everyone has the freedom to do absolutely anything they want—they might just get thrown in jail if it happens to violate a law. This makes a mockery of the very word "freedom".
If the law says that an action can lead to you being put in jail, fined, or otherwise deprived of your legal rights, you aren't free to do it. "Free" means "no strings attached". Within the legal domain, naturally; the freedom of speech has never included protection against possible social consequences. Others have every right to respond with speech of their own, or to withhold their support or association depending on how they feel about what you've said.
It's funny how everyone turns to the "fire in a crowded theater" case when discussing the limits of freedom of speech, because in addition to being logically unsound, that ruling was politically motivated with the clear intent of suppressing political speech by war protesters (Schenck v. United States). In other words, exactly the opposite of what freedom of speech is supposed to stand for, even by the strictest standards.
If the speech is false, and deliberately intended to manipulate others as tools for causing harm, not by their choice but by the choice of the speaker, and the actions these others chose to take based on the speech would not have been harmful if the speech had been true—then we can discuss whether a punishment is justified, not for the speech per se but for the harm that the speaker deliberately set out to achieve. But "(falsely) shouting 'Fire!' in a crowded theater" is not that case. Whatever the speaker's intent, the actions of the listeners were not reasonable or justified even by the standard of what they believed to be true, and it is those unjustifiable actions which resulted in the harm, not the false speech.