Please read more about speech and genocide. The Bosnian massacres and Rwanda are two examples of people being urged to violence by speech. SCOTUS also recognized the problem of speech to incite violence. There is a VERY well known problem of tolerating the intolerant and many liberal thinkers have argued that it's not valuing the right to speech to leave a field for speech that destroys freedom itself. Nor does an atmosphere of threats and violence create the conditions for free speech.