Most taggers are just high schoolers pissing on stuff to mark their territory with spray paint and permanent markers. The worst are idiot taggers who etch windows, doing hundreds or thousands of dollars in damage, or who mark up the insides of bathrooms and the like. I don't really care if a tagger hits some concrete wall next to the freeway. More power to them. But the other are just a-holes who should be treated just like someone who throws a rock through a window or slashes tires.
The best tag I've seen in a while though was on a closely sheared arborvitae hedge near the Hollywood Fred Meyer. I've been enjoying watching the arborvitae grow out and the tag disappear. Allow. However, that is my only exception.