FWIW, there's plenty of publicly-sanctioned art that is a crime, IMHO...

And not to condone vandalism, but... some graffiti, like the NY subway car exteriors done "back in the day", or the work of someone like Keith Haring, can lend a lot of life and color to public urban spaces. When a municipality encourages such expression and finds a creative way to allow it (like the Chicano Park in San Diego, which features some amazing stuff), it's a civilizing factor to a community.
What ticks me off is when some brats put their lame tags on any blank surface, even the walls of private owners who can't afford to keep re-painting them... like dogs peeing to mark their turf. I haven't seen much "tagging" that's more worth looking at than a pee stain.