When I read this, I thought it curious that if we were to replace "Christian" with "adult"--adult writer. adult movie. adult literature. adult environment--there is no ambiguity, even though "adult" is a euphemism.
The reason "Christian" as an adjective is ambiguous is two-fold. First, in common parlance, "Christian" covers every way of thinking from Westboro Baptist to United Church of Christ, so that practically any stance can refer to itself as "Christian," regardless of doctrinal integrity.
Second, "Christian" in the arts has become, not only a statement of theology, but a statement of niche marketing. It is presumed that only hardcore Christians will read "Christian" novels, listen to "Christian" music, and watch "Christian" movies, and certainly no one with a truly literary or (educated) musical bent would deign to stoop so low as to sully him/herself with such pandering-to-the-pews drivel.
Second, "Christian" in the arts has become, not only a statement of theology, but a statement of niche marketing.
Very well put.