Graffiti, is it really bad?

Yesterday, I noticed a piece of art work on a wall of a community center. Some may say this is a criminal offense but I was amazed at the detail and skill that went into this visual display.
Originally graffiti was began in America in the late 1960's by street gangs to mark territory, it also was used as a means of gaining attention from the local community as well as the press by political activists.
By the early 1970's writers of graffiti were becoming well known for their specific style. The subway system became an important line of communication with regards to graffiti and people from neighbouring communities became aware of the different themes within the graffiti, its style and message.
Now graffiti is an art form with its own terminology. Writers have developed a 'tag' which gives an indication to who the artist is, by using flourishes, stars and other cartoon images.
I think it is definitely art, a form of expression for all to share and at least it adds colour to some of the run down buildings. I think that graffiti is only effective in small amounts, if it was displayed in excess, it would lose its meaning and become unsightly.