I have to admit what you're now saying is coherent. Basically you're making an argument that whether you're gay or straight has a "nurture" component to it. That some people are totally gay, some are completely ...
It wouldn't make sense for Purity's libido to get triggered by Mommy playing virgin with Daddy (ick).
But we can introduce Purity's best friend (we don't need to call her Chastity), the preacher's daughter, ...