That behavior of his, to use women as "sex toys" (your term, I think, not Rich's) takes a while to come out but by the time the arc in BRiTF ends, you can look back and see that pattern as a part of Tarqins overall consistent pattern of behavior: he is a user of people to include his own kids, (and all 8 or 9 of his wives?) and his associates from adventuring days ... when he can get away with it.
You may be surprised to learn that there are also racist sorts who will not even consider such a liaison, even an abusive one, due to race: as I was growing up I encountered no few people like that - but that's some IRL stuff that we'd best not drag into this discussion that might be getting close to the edge of forum rules anyway.
(PS: your "therefore" does not necessarily follow, but it can follow, certainly)