Sounds like some people here need an English lesson:
I know that's lots of big scary words, so I underlined the important ones.
This "tagging vs. art" discussion is a complete nonsense. You either have permission to apply paint or ink to a public surface, or you do not. Whether the result is 'art' or not is another question entirely. An illegal piece of graffiti may be a modern masterpiece, and a publicly sanctioned mural may be a complete eyesore.
On a related note, I remember many years ago the Melbourne City Council installed 8' by 4' "art boards" in the city square so that spraycan wielding artists could show off their stuff. These, of course, got vandalised, became a catalyst for violence, and were ultimately removed.