Personally, when I am asked why I open carry, I answer based on who is requesting. If it's a cop, I typically give a wry grin and obviously glance at their open-carried firearm. They typically then respond with "I'm required to do that". To which I ask "why do you suppose they require you to open carry?" To which they give a miriad of reasons. Then I just say "those sound like good reasons to me." In another such instance, a cop said "but wouldn't it be better if you concealed?" I said, "I will conceal when the law gets rid of my requirement to show ID and a permit in order to conceal. I don't like being harrassed and value my privacy. Oddly enough, law enforcement in cooperation with legislators created this problem when you created the need to have a permit to exercise my constitutional right. Drop the permit requirement and I'll conceal." He responded "DO YOU have a permit??" To which I said "now you see the beauty of open carry. I can tell you to pound sand because it's none of your god damned business while I'm open carrying, is it?"
Yes, I know those of you who feel we should always be polite when open carrying, and I usually am to the every day citizen. I refuse to be polite to police any longer.
All others who ask about why I open carry are responded to based on their demeanor and willingness to actually hear the answer.