What's the Point?

Graffiti and public art pieces seem to be everywhere in this day and age. Not because all of a sudden it came up, but because we have the internet to see it all at once instead of coming across it on the street. It also has begun transcend from the streets to pop culture; being brought into mainstream society by big names like Obey (Shepard Fairey) and Banksy. I have been doing research about said topic and have found some very interesting and surprising pieces of information. I have read books, articles, and watched videos and documentaries of graffiti artists talking about their life and their work. 

I have always loved all sorts of art, but this was one kind that started to catch my attention at the beginning of my high school career. I had never taken it seriously until then, when I watched Exit Through The Gift Shop, a documentary about graffiti and public artists. Though the legitimacy of this documentary has been debated since it's release, it got me thinking about it as an actual art form, not just as a kid righting on walls. Lately, however, I've been thinking about what was the reason for all of this art. What's the point? To get to that answer, I feel that I have to first explore when and why it started, and how and why it became mainstream. With a subculture now becoming part of pop culture, is part of it's original essence lost? Or is it just an inside joke that only certain people know the punchline to? Can any of these questions even be answered?