As for fornication, there does arise a problem when there is a significant (or perceived to be significant) power difference between them, so that the weaker was intimidated or thought she could not successfully rebuff the stronger.
(Just listening today to a Scots Gaelic Waulking Song on YouTube, "My Father Sold Me to a House of Sorrow" --- a lament about an arranged marriage. Hm.)
From a plain human decency point of view, nobody should have sexual intercourse with anybody but their honest-consenting, honest-wedded spouse.