Well...

We are a visual society, let's just face it. So is a visual argument more persuasive than others? I believe that it would first of all depend on the audience. If the audience is a younger crowd, yes, a visual argument will hold more power than if the audience is older.

Nobody talks anymore. Picture texts, commenting on albums on facebook, photo shopped news pictures...its all images. This generation is becoming one of images, and not much else. When trying to reach the youth in America, you would be more likely to get their attention by putting out a controversial image to the media rather than making a speech. (Ugh, words, how boring)

Basically- visual arguments are the way to go in today's society. While there are other effective methods of making an argument, this is definitely the best and easiest way to get through to the pea sized brains of today's generation.