Yelling “Fire!” in a crowded venue is not protected under Free Speech.

I know that’s the famous example, but you’re actually wrong. It’s only not protected if there’s no fire, the person yelling it believes there is no fire, and the person yelling it is doing so to cause a panic or imminent lawless action. Speech protections in the US are extremely broad, and most of the exact lines and contours have been defined in court, often in cases involving the ACLU, the KK, or both (specifically in the form of the ACLU defending the KKK, which is where many of the lines as regards protests were determined).