Gotta hand it to the authorities. At first, I was mad when they scrubbed the Banksy, but they have unintentionally made one of the most powerful artworks of all time.
Everything they do to hide or erase it makes it look more poignant than the original.
I'm gonna guess that if they'd spoken with Banksy's team, they'd have told them a simple cleansing solution that'd have had wash straight off. But they piled in and used regular chemicals that just stained it worse and drove the paint into the pores of the stone.
Lady Laura 
In Search of a Better World