Full Idea
One case when the depiction of immorality becomes an artistic flaw …is when it is presented in brutal detail in a way that glorifies it. The celebration of evil corrodes the work's artistic value.
Gist of Idea
If the depiction of evil is glorified, that is an artistic flaw
Source
Stephen Davies (The Philosophy of Art (2nd ed) [2016], 8.7)
A Reaction
This doesn't allow for the case where the evil is celebrated in one part of a novel, yet the novel as a whole does not endorse the evil. The Marquis de Sade seems to have fully celebrated what we take to be evil.
Book Reference
Davies,Stephen: 'The Philosophy of Art (2nd ed)' [Wiley Blackwell 2016], p.216