The Achilles heel of your argument, Gary--and really the whole liberal position on speech--is in underestimating the irrational aspect of political discourses, especially those like white nationalism that rely on something very like tribalism.

Science is only now coming to realize how much the unconscious mind, not reason and rational argument, influences decision making. Advertisers have known this for years. 

People who FEEL the white supremacist message are going to identify with it no matter how valid and reasonable the counterargument. Bannon and the alt-right KNOW this in their bones. 

This makes them much more dangerous than is accounted for in ACLU-type defenses of hate speech. The world has changed since those defenses were conceived.