My point is that the way to settle the "illegal graffiti art over illegal street art" ethical argument is to defer to the owner of the property--he alone can legitimize one, both, or neither artist. Legitimacy doesn't depend on some strange need to assess which "scene" is more authentic or otherwise meritorious.

And I can't tell if I've made myself sufficiently clear, I have no special affinity or animosity for Banksy or any other modern artist.

I 100% agree.

The owner decides what stays and goes. It is theirs.

It's just complicated since the first person attacked their property. The second also, so the third, and the third might be the one they like the best, not the forth.

The doco I link is fun. It's a not bad Friday night viewing.