I think graffiti can be a form of art, same with tagging a building. It's all about how it's done and what message is being conveyed. Graffiti art can be incredibly moving. I think a lot of artists go by pen names because they don't want their background to interfere with the way the person views their work of art. When you don't know who produced the work of art then that gives and illusion of mystery to the person viewing the art. It strikes questions and can move the person in a more dynamic and open minded way.