Ascentia is exploiting Twilight's guilt to keep their marriage from ending. The abused has become the abuser.
Equestria's seemingly lax sex laws seems like a Word of God issue to keep legality out of the way of the story's more smutty scenes. Then in Illicit Disco it's revealed that Vankanir, Equestria's primary ally, considers Equestria to be an abhorrent pit of debauchery. In fact, most countries, despite loving the country's foreign policy, consider Equestria to be second only to Karadun in terms of disturbing sex laws. Then we remember what Princess Celestia said about having urges regarding her young students... oh dear.
Rainbow's issue with ephebophilia seemed to be treated during her time in the mental institution... until her son grew up to be a rather feminine person. Additionally, nobody else raises an issue with the fact that she's sleeping with her son, but were very angry with her when she attempted to sleep with Sweetie Belle. Especially Ascentia, who threatened to kill Rainbow after making a pass at Sweetie Belle, but regards her activities with Spectrum to be cute. It's almost as if Equestria doesn't take the abuse of men seriously or something.