Oh, brother!  Harumi is more old school than I thought.  True respect is earned by everyone BEFORE being given to anyone!  No exceptions.  What Harumi is describing sounds more like fear-induced courtesy based on intimidating size difference.  Hence, the so-called "disrespect" notoriously exhibited by teenagers to their parents.  After all, why continue looking up to your parents when you no longer have to look up AT them?

As to this form of enslavement being kinder and gentler compared to being lab specimens?  That's debatable.  I'm dead certain that was just a convenient rationalization for Ayumi and Harumi, right from the start. They had no intention of doing anything but enslave Mike and Jennifer as living novelties!  Ayumi, especially, as she didn't want to miss any opportunity to move out of the old family homestead and gain her own independence (financial and otherwise).  Hence, the indisputable abduction of two people with no other choice but to lavish attention on Mama-san...in exchange for not being tortured.