Nothing wrong with the art of spray paint, as long as it’s legal.
Just random vandalism isn’t okay. Some punk sprays a tag on the side of a building owned by a small business and that business has to pay out of pocket to get it removed, if they can afford it. And the pony that sprayed? Their work is removed! Or sprayed over with another tag. So why even do that?
A graffiti artist doesn’t have to make a mural, either. Art is art, as long as it’s legal.