I have always hated graffiti. In my small Ohio hometown, there was always one small, out of the way underpass that was covered in it. There, and only there, kids knew that their "art" would be untouched. So it tended to contain itself and it seemed to be limited, more or less, to local high school rivalries. But even then and in that limited context, I found it ugly, disrespectful, and obnoxious.
But now I live in Los Angeles and I have seen this policy of tolerant containment prove to be pretty ineffective. The rivalries here are stronger and over things much less innocent than which high school football team is the "baddest". Sometimes it involves gangs, and sometimes just bored kids with nothing better to do and no one intelligent enough to give it to them. Whatever the case, it scars the community and supports a culture of slovenliness, disrespect, and despair. Nevertheless, it continues to have its advocates. This link is courtesy of a relative who is a long-time employee of Cal-trans and has a very different view of these matters than the one described here.
To call these vandals "artists" (whatever their accomplishments post-criminal activity may be), strikes me as patently goofy. Why glorify something that is so destructive to the rights of others? Why glorify something that is so destructive to the well-being of the community. Rudy Giuliani’s "broken windows" theory is absolutely correct in this instance. If people want to paint in a graffiti style--God bless them. But get some paper.