Graffiti as an expression of social identity

In the movie Style Wars, different aspects of the topic of graffiti are presented: the graffiti writers’ attitude that they are expressing themselves, that what they are doing is art; the attitude on the part of the city officials that graffiti is vandalism and that it is a public nuisance that is expensive to remove. What are your feelings about graffiti? What do you think of the idea that graffiti is an expression of social identity? Does anything justify the fact that it is illegal? Be detailed in your response (200 words minimum) and feel free to include any examples of graffiti that may illustrate your point of view.