Don't bother. This is a person who has already made up their mind and will not listen to reason. It doesn't matter how logical an argument you present, they will counter it with misinformation. Usually some crap about, "You'll be the first one shot, someone will try to take it, extra attention from cops, element of surprise, etc."
Now if someone approaches you with something like, "Why do you open carry?" or another open ended question then absolutely take the time to speak with them. This is a person that is demonstrating the will to actually listen to what you might have to say.
I have rarely encountered negativity to OC and that's with living in the uber liberal Puget Sound area of Washington State.
Just the other day I OC'd into a mall and had zero issues. Even had a security guard walk by me. He looked right at my gun then tipped his hat and said, "Good afternoon, sir."
I nodded and smiled, "You too, sir!"