Graffiti has always had a bad name in the art world. Some do not consider the painting and scrawling on the wall art at all. Others complain about the ruination of private property and the cost of clean up. But you look at pieces by Bleck le Rat and Banksy, or the even the iconic "Hope" poster used by the 2008 Obama campaign, and you get a different understanding of "tagging."
But not everybody is Shepherd Fairy, and not everyone does this as art. Some people just plainly do not put any effort into it and so you get this gallery of Awful Graffiti.