There are many schools of thought about graffiti. Is it art only when it defaces property and has a taste of illegality and property destruction?
Or... is it only art when there is no harm and it can be judged solely on its artistic merit?
Here are a few intriguing perspectives on the idea...
Both Sides: The DEBATE
This one tends to say YES it is art: Art Through Vandalism
This article looks at both sides: Rethinking Graffiti
This post thinks Graffiti is NOT art: POSING AS ART