Banksy's quote is quite ironic, coming from a guy that's well known as a master of publicizing his own work... even more, doing that by creating/exposing his work in "public space", using the walls of private and public buildings as a canvas without asking anyone for authorization.
Anyways, property can still be argued about, and cities will make laws to make sure nothing gooes out of control. I prefer seeing graffitis than large ads.
Yep, cities may have regulations for that, and they usually do these days.
And I don't necessarily agree with your preference. My family used to own a large, historical house that had a huge front wall because the terrain was very elevated from street level. And I can tell you from experience, most "graffiti" is worthless crap scrabbled by drunk teenagers without ANY artistic talent or ANY worthwhile message to the world. If you give graffiti a pass because there's the one-in-a-million Banksy, you should also tolerate ads everywhere because a few of them happen to be awesome.
