I think it depends on what is trying to be accomplished. 3 things struck me right away. First is that it would be nice if we lived in a world where you could do that and it wasn't a news story. Just somebody going about his business in a lawful way. (True, it was a demonstration of some sort, but the idea holds). Second, I don't think most gun rights people will bat an eye at this. Third, and this is where the goal of the OC'er really matters: It was an over the top demonstration which will probably solidify the anti-gun nuts in their opposition. A subtle approach is sometimes more effective than an in-your-face approach. For those people who simply see a gun and are terrified, this won't do much to convince them to come over to our side. While the guy was certainly within his rights, I don't think he will have swayed one person's opinion.
As an example I would offer the abortion issue. I believe many people who are against abortion are also against the tactic of sticking pics of aborted fetuses in people's faces or on picket signs. While those images may be factually true, it's the methodology that disagrees with people. I don't think this is altogether different.