You have to appreciate the paradox of Banksy: A commercially successful anti-capitalist. A vandal who adds value. It's the sort of amusing contradiction that appears often in the artist's own work.
A case in point: In 2009 Banksy made a wall painting on an industrial estate outside Croydon, South London, depicting a spike-headed punk rocker puzzling over a set of instructions. Next to him is a box labeled "LARGE GRAFFITI SLOGAN," with a jumbled cargo of words--"SYSTEM," "SMASH," "POLICE"--spilling out, waiting to be assembled. The logo on the box is also disassembled, but easily recognizable: IKEA.
The guerrilla artist had barely finished his mural when a pair of guerrilla businessmen swooped in, subverting the subversive message. It's an interesting story, nicely told in this nine-minute film produced for Channel 4 by Martyn Gregory, shot and edited by Paul Bernays and narrated by Nick Glass.