I am getting low on argument juice.

   This new proposal is based on the work of a modern artist named David Banks. The english call him 'banksy'.  In my feebl opinion, Banksy is among the world's greatest humans because he fearlessly humiliates the establishment.  He has been known to smuggle fake exhibits into museums and place them where they are taken as real by visitors. Banksy purchases paintings at local markets and adds to them in order to make the paintings more relevant. He is known as a graffiti artist among other things. He has a fabulous sense of irony.

   I am not putting a link here, but you can get to his site by adding www. to banksy.co.uk

  Is banksy justified in doing what some people call vandalizing other people's art?

I can't say, from theory. I'd have to experience the result.