Oh, I don't disagree. In fact, I would be willing to bet that one of the reasons he uses stencils and the medium of street art as his vehicle for high art is that very idea that separating the work from the artist is, if not impossible, very very difficult. This is something that Duchamp played with extensively with his readymades, which still upset and even anger people. I have to wonder what it might have been like for artists like Duchamp or Magritte if they'd been born in the era of streetart, computer manipulation and the internet.
I think Duchamp would have had a ton of fun with the internet. I think Dali would have found a way to make even more money with ridiculous stunts and frauds. Not sure about Magritte. I have seen a few exhibits of his, and I think he creates fantastic imagery, but I can't profess to know too much about him and his motivation. I think Banksy read the Fluxus Manifesto (pictured below) and thought to himself, "Well these guy were right, but why did that have to create such shitty art?" So he decided to do something about it.
Haha, it often seems like those that write manifestos end up creating shitty art, or art that doesn't really appeal to many people. Ideas and execution need balance. That balance is struck through feel and feedback. It's tough to get good feedback when you've issued a manifesto that is likely to provoke strong opinions about what you may yet create.