Graffiti is art, isn't it?

How much graffiti is acceptable for a city? Should we admire it as art? Or is it plain vandalism? Read this article for an insider's view:

http://www.theguardian.com/artanddesign/2013/jun/21/my-secret-life-graffiti-artist

Perhaps this article about Banksy, the famous British graffiti artist would interest you as well: http://learnenglishteens.britishcouncil.org/uk-now/read-uk/graffiti-art-or-vandalism