What if the artist wants to self-censor? For example I personally think Max Brod was acting unethically when he didn't burn Kafka's remaining work. The world is a better place without Kafka's art, and in his darkness Kafka recognized that.

Art can be pernicious. When cognitive scientists eventually figure out the physical mechanisms of human dreaming, will it just for artists and the corporations that employ them to make art in other peoples' dreams? Advertisments are among the most common form of art. Should all advertisments always be permissible because they are art? I think that as ads become more and more effective and sophisticated, questions of invading other peoples' consciousness and will become more vivid. Particularly since advertisements are almost by definition oppositional to the goals of the individual -- the ad aima to change the individual's mind or attitude.

And what about art in war? The current fad of drawing the prophet of Islam just to see how violent the reaction will be seems clearly to be an extension of the crusade being waged against Islam. What if an artist is an agent of say the CIA, and their art is specifically intended as a weapon? (See The Cultural Cold War for a history of the CIA using arts and culture as weapons). Do nation states get to make any art they want in the name of war? What if the art is propaganda and leads to the dehumanization of an entire people, who then in reality are subject to genocide or mass deportation?

As an artist, I think censorship is a natural part of the artistic process. If an artist wants absolute freedom of expression, they can wander off away from other people and share their art with the silent kosmos. If an artist wants to engage with society, they must accept that their expressions have larger effects, often unforeseeable, and that their artistic freedom is not infinite.

In a just society, artists should probably respect the laws of censorship. In an unjust society, censorship should be fought and challenged. (see Rawls for the general distinction). But generally, I think it's a huge error to consider art to justify itself without external qualification.