Full Idea
Moral value is valuable in art because people care about moral value. This runs deep, but it is a contingent matter, and the value of morality in art hinges on art's need to provide something precious to us.
Gist of Idea
We value morality in art because that is what we care about - but it is a contingent fact
Source
Eileen John (Artistic Value and Opportunistic Moralism [2006], 'Contingency')
Book Reference
'Aesthetics and the Phil of Art (debates)', ed/tr. Kieran,Matthew [Blackwell 2004], p.341
A Reaction
I think this is exactly right. Thrillers are written with very little moral concern, for a readership which cares about brave and exciting deeds. Even there, violence has its ethics.