Graffiti works on soo many levels...
graffiti employs soo many people, it gives jobs to immigrants and other people who would probably be on nthe dole, ie buffers, it also gives older people a contravertial topic to bag teenagers for and provides eye candy all along the train line.
Just think, every time you do a tag, you can say to yourself " I create jobs, I'm helping put food on the table for someone out there."
HAHAHAHAHAHA