You’re right, but you have to draw the line somewhere. If someone decides to light a building on fire and call it “performance art,” nobody considers it anything but a crime. If someone spray-paints a vulgarity on the side of a school, few would call that “art,” but a mural on the side of a concrete wall is “street art.” The subject matter and the quality of the painting doesn’t make the determination between art and vandalism; it’s just vandalism.