I think EY's central point is something like: just because there's no built-in morality for the universe, doesn't mean there isn't built-in morality for humans. At the same time, that "moral sense" does need care and feeding, otherwise you get slavery - and thinking spanking your kids is right.

(But it's been a while since I've read the entire ME series, so I could have confused it with something else I've read.)