Argument #3. Open carry is a bad idea because visible firearms clearly deter the free expression of ideas.
Finally, the left has admitted that deterrence theory has merit! These guns that somehow don't deter murder and rape actually do deter conversation. To recapitulate, a gun won't save a person from being attacked but it might prevent his ideas from being attacked.
The fun thing about leftists is their endless supply of cognitive dissonance. As such, there are always plenty of opportunities to find the contradictions in their worldview. This is fun for a while, but it eventually becomes tedious, much like dealing with a toddler.