@BraveHeartedHero the point is that they made her a slave because they were lazy and didn't want to write a legitimate romantic connection, so instead she instantly has to obey him and is totally fine with everything, and later on perfectly willing (and eager) to enforce his will on the other girls. It is so. damn. lazy.
Imagine instead they meet in the dungeon and hit it off, date, grow attached to each other. Later on as she learns more about him and his goals they open it up to meeting more harem members and repeat the process.
Instead, he is going to use cheat powers and grind money to buy more women.