The word vandalism is a derivative of the name of a Germanic tribe, the Vandals. The meaning of vandalism comes from their alleged sacking and looting of Rome. The Vandals – ruling Carthage without bringing on much destruction, whilst the Romans razed the city and sold the entire population into slavery – was probably not anything worse than the rest of the Germanic tribes having a go at Rome. Someone just had to take the blame I guess. Anyway, vandalism as a word was coined to refer especially to the destruction of artwork following the French Revolution.
Given this meaning of the word, I will not point to street art as vandalism. Street art is civilized culture. Street art is trying to correct or make bearable the true vandalism, the cheap concrete and asphalt brutalism that has governed our urban development since WWII. The city is planned and built without too much regard for aesthetics or the human scale. It is built for high profit, cheap rent, cars, easy entertainment, muzak, shopping, dust and pollution. Aesthetics is reduced to prettiness, ornaments and garniture.
Street art may fruitfully be seen as bringing the human scale and aesthetics – in the true sense of the word – into this scene. In this respect, street art is a reaction to the barbarianism of urban development driven by capitalistic ideology, and an administration and politicians lacing equally visions and balls to correct it. Street artists may not always ask for permissions, and they may have a general disrespect for private property rights regarding the decoration of facades, but they are not vandals – quite the contrary.