I consider graffiti as a powerful type of art. When I think of graffiti I think of those beautiful and colorful artworks with a social meaning or simply which are able to evoke some feelings in people who observed them. Moreover a graffito can be a symbol of a city or a country and can transmit a particular culture or way to see things. 

Looking at graffiti we could probably change our mind and get an other perspective to see the world. This is the reason why I say that graffiti are powerful. Certainly a graffito has to have a sense and a context. For 'context' I mean a particular background in which is allowed to exist. Otherwise a graffito has no value at all. 

The line between art and vandalism must be clear: a graffito which covers abandoned areas or adorns some particular places has a certain value, instead a work made with no sense or aim, only disdaining something or showing no regards towards communal goods has to be banned. Often people used graffiti as a mean of criticism. This can be done but always in respect of the limits in terms of other's freedom. If a murales coveres some social building, museum or monument has to be punished because it does not respect the other citizens first and then the object itself as a product of another man. As Giovanni said, graffiting on the Berlin Wall are admirable because it is great a collection of artworks and cultural exchange. In that case the context  is perfectly appropriate and I remember when I came to visited it made me feel completely immersed in the history of people, more than thousand of words.