Let's not kid ourselves. Graffiti is, in fact, a private form of expression that's done in a public space. Leaving aside the sticky questions of using someone else's property as a canvas, it can still be said that the vast majority of it just isn't that good. Yeah, there are some incredibly talented and innovative artists who work in graffiti. There are also a whole lot of hacks whose talent for expression doesn't extend past scrawling their names on someone else's wall.