This is a criminal matter, not a civil matter. It's just like if a guy punches me on the street, but I decide it was cool and edgy and added to the gritty vibe of the neighborhood. The prosecutor can still bring charges.
Surely not. Better question: is "vandalism" without criminal trespass or property damage actually a crime? If it's on private property, and the property owner enjoys the painting, it seems like it'd be quite a stretch for the state to establish that the artist damaged the property by creating it.