what's wrong with graffiti?

Maybe this is controversial, but I'd just about a million times rather look at some sort of graffiti than yet another giant ad. I somehow got on some weird random mailing list for San Francisco city politics (strange, particularly given that I don't even live in the city of San Francisco but rather about thirty miles south), and there was this message about a meeting for the graffiti abatement program. They have all these people who go out and get rid of graffiti as volunteers, and I totally don't get it. Ok, I wouldn't want everything to be covered with tags, nor am I suggesting that having every business or home covered in graffiti is a good thing. But seriously, lampposts? Random half-empty buildings in deserted parts of town? Freeway overpasses? Bring it the fuck on. If I could exchange every billboard and bus station poster and other form of advertising intrusion for graffiti, I'd do it in a heartbeat.