I'm going to speak my mind, so this won't take very long. Graffiti is not the lowest form of art. Despite having to creep about at night and lie to your mum it's actually the most honest artform available. There is no elitism or hype, it exhibits on some of the best walls a town has to offer, and nobody is put off by the price of admission. A wall has always been the best place to publish your work.
The people who run our cities don't understand graffiti because they think nothing has the right to exist unless it makes a profit. But if you just value money then your opinion is worthless. They say graffiti frightens people and is symbolic of the decline in society, but graffiti is only dangerous in the mind of three types of people; politicians, advertising executives, and graffiti writers.
The people who truly deface our neighbourhoods are the companies that scrawl their giant slogans across buildings and buses trying to make us feel inadequate unless we buy their stuff. They expect to be able to shout their message in your face from every available surface, but you're never allowed to answer back. Well, they started this fight and the wall is the weapon of choice to hit them back.
Some people become cops because they want to make the world a better place. Some people become vandals because they want to make the world a better looking place.