Dreamduke nails it. Rather wonderfully, what he's describing is vandalism against graffiti itself. When something is erased it has been affected by some other object. Apropos of my previous.
Because there is a profound ambiguity in objects, which is precisely the chorismos between their being and their appearance. This results in appearance having a slightly evil vibe about it, according to some philosophical views. Because you can never be sure. Is it art? Is it vandalism? We can ask this question because art is always already vandalism, causality...