Contemporary graffiti is essentially a form of painting. The methods and materials of painting are the same, therefore, specific examples of graffiti would be assessed as art or not art by the same standards by which a painting would be assessed.
For example, a crude tag involving a person spray painting their name is no more art than a someone who signs their name on a canvas using a brush. Given that graffiti is in essence painting and it involves the very same techniques and mediums as “conventional” painting, the proof would seem to be on those who would deny that graffiti is.
Can graffiti be art while maintaining that painting is art?