This is a game for adults with adult themes which include slavery, body horror, murder, cruelty, the killing of children and you are upset about some "mild" sex with a horny/manipulative Drow that you have to take a specific evil path to even get to? Ok, that seems totally reasonable.
Minthara and the Drow in general use sex like a weapon, to control and get info and manipulate people, which is exactly what she does. It is an accurate portrayal of their culture.
