Graffiti is one of those signs that were always indicative of social blight in urban centers that it has become natural to look at it as an societal ill and sign of an underlying problem. However many people are starting to look at graffiti in another light and considering whether or not it represents art or can provide some deeper meaning.
Reasons why graffiti is art
Art, at its base level, is the manner in which a person tried to express themselves thorough some type of creative endeavor. In this regard graffiti surely qualifies and fits into this definition and qualifies as an artistic piece. This can be even more obvious when one looks at the more magnificent pieces of graffiti out there that can be creative and challenging and have unique and interesting elements.
Graffiti is not art and should not be tolerated.
Those who create graffiti are more interested in destroying the sanctity and cleanliness of an piece of architecture and city facade than in creating something artistic. The question of whether graffiti is art is akin to asking if a person carving their name into a tree is art or simply something that is an annoyance or distraction. In a way graffiti can be thought of as a destructive force on a piece of architecture and therefore viewing something that damages another form of art is an extremely tenuous path to start to walk down.
Ultimately where you stand on whether graffiti qualifies as art has a lot to do with both your conception of art as well as how qualified the graffiti artist is. People come to their own conclusions quickly and permanently on this topic and few things can sway them. Though the extremely polarized attitudes on the topics can show some artistic qualities in that it gets viewers to think about what they see and to determine how it fits into their city.