The Image is so ubiquitous today that it has numbed us, that is, until we see the unfamiliar image which we usually call Art. In this sense, it is unnecessary to worry about The Image’s overusage since this actually gives all the more Art its strength.
The point of Banksy’s art is social commentary. More importantly it is location specific. So by removing it from the wall it was painted on means it loses its meaning, significance and value. In a sense Banksy is really criticizing about this kind of phenomenon by choosing graffiti as his medium.