At the risk of opening a can of worms here, it -is- pretty hard to by even supervillain standards to justify that particular crime. Murder, you can justify by self-defense. Hitler justified genocide in the name of racial purity. Rape... you can't really justify for anything besides getting your own personal drooling jollies off someone else's misery.
You could argue it's a way to "break" someone or screw with their minds, but there's plenty of ways to do that that's a lot more horrifying and effective, without painting the picture for the community at large that you can't keep it in your pants. In a Catwoman issue, Black Mask cut up a prisoner's S.O. at one point, then forced her to eat the pieces (never outright stated, but heavily implied).