I’m in the process of making my way through Painting without Permission: Hip-Hop Graffiti Subculture  by Janice Rahn and Graffito  by Michael Walsh. The former is lots of text and the latter is lots of pictures. I feel like I've spent way too much time trying to understand graffiti, specifically tagging, and perhaps I will never truly understand it because I am not writing in their shoes, so to speak.
Putting aside the illegality issue of tagging, I'm simultaneously intrigued and repulsed by it. Intriguing is the idea of distilling yourself and your message to a series of letters or symbols and putting it out there, everywhere. "I'm here! I'm alive! I did this!" The inventiveness and beauty of some of it. The idea of celebrating the alphabet and putting letters together in new ways.
Repulsive is the repetitious nature of it, the ugliness of some it. Writing a tag over and over again would give me brand fatigue. But, from what I've read, it's anything but fatigue, there is excitement and a high that comes from the creative destruction process. Some describe it as a meditation. The purpose of taggers are numerous and vary: to get their tag up as much as possible, to be seen in interesting locations, to win the respect of the community, to communicate an idea.
As my role as a viewer (neither tagger, nor authority) there is a fine line. Some tagging is, dare I say, okay and thought provoking. Too much is ugly and makes you feel like life is out of control. It's great that the tagger had his (most are male) release at my visual and, ultimately, financial expense (my taxes go to clean up).
Under the new Mercer Underpass