Just to mention, the bloke whose wall Bansky used in Folkestone is absolutely over the moon. Another bloke I know there wishes it was one of his walls that got "defaced". Visitors are flocking to see it and spending good money in the coffee shops, pubs and restaurants. Everyone's having fun.
Of course this is in a town where the conscious regeneration of the place via investment in art has been seen to make a big financial and civic difference so people's attitude towards it is much more playful, accepting, and open - as well as grateful for the dosh.