Some people say "this is just fiction, not revelation!" And yet, the tradition says that these bawdy plays were established at the command of the gods. If nothing else, the lack of recrimination from the gods would seem to imply their consent. And while it's true that some plays are not so lewd as others, it doesn't change the fact that they're all teaching immorality.
Not to encourage anyone to morality, but if you want my favorite example of one of these plays, check out Aristophanes' Lysistrata.
Even the ancient Romans understood this to some extent, since they forbade what was said about the gods to be said about living Roman citizens. (Unlike the Greeks, for whom everyone was fair game.) This shows that they knew the true moral worth of the plays and were just inconsistent in their application of that knowledge.
The spirits behind the plays (Augustine says "demons", but I don't know that it is any different if only human sin is in question) don't care that they are being defamed, so long as human sin increases: "But the devils... are content that even iniquities they are guiltless of should be ascribed to them, so long as they may entangle men's minds in the meshes of these opinions, and draw them on along with themselves to their predesitnated punishment." Such is the nature of sin that at the end of the day it doesn't even care about truth, it just care about rebellion against God.