Mark Holsworth is apparently a much more eloquent writer than I am. On his blog, he makes some great points about why the misconception that street art cannot be brought into a gallery is just that: a misconception.
Here’s my favorite point:
Walking through W.E. Kennick’s imaginary warehouse of all the objects in the world and trying to pick out the art you may be confused by Duchamp’s readymades but not by the street art. (Kennick, Journal of Philosophy, v.81) Street art is designed to appear as art without the museum, you would know that it is art anywhere.