I don't know who Banksy is, but I have seen some graffiti art that is truly beautiful.

For the stuff that is not beautiful, I figure it is probably just practice. Maybe the artist will be good someday. Everybody has to start somewhere. The first song you sang probably wasn't beautiful, either.

Even if it's mediocre, it's probably an improvement over the average boxcar or blank industrial wall.

Graffiti art is different from "tagging" which is how gangs (and their imitators) mark their territory.

I suppose the owner of any property has the right to prevent unauthorized people from painting it, but I wish more property owners would allow and encourage it.

I strongly disapprove of laws that require property owners to remove or paint over graffiti, or that impose penalties on graffiti artists even when the property owners have no objection to the art. Such laws seem to me an infringement of the right to free speech.