One man's terrorist is another man's freedom fighter. Every noteworthy push for societal change through history that ever involved breaking a law could be labeled vigilante behavior by some party. I just don't find that argument convincing. Our laws aren't there to protect themselves, they exist to create the society we want to live in. In what ways did the artist's actions harm our society? In what ways did it change how we view our society? Do we like what we see?
This isn't big brother with all the power systematically spying on citizens, this is a nobody with no power showing us a picture of ourselves. Both cases are happening, both happen against the will of the people, and yet which one do we allow to continue?
I'll also point out that the discussion we're having is exactly the outcome the artist intended.