This is one of those studies that I'm not sure are profound or silly. But of course people changed their minds after listening to a reasoned discussion, who wouldn't? The more interesting case would be "people impervious to written communication".
What I'd like to know is whether people changed their mind or changed their worldview, that is, do written pieces actually get people to think radically-different about major parts of their lives? Or do they just get people who are a bit apathetic more energized and sure of themselves about something they're already predisposed to generally agree with?