In "Doctrinal Discussion" Jason Lindahl writes:

In fact, progressive society now tells us that the basic parts of a family machine are no longer necessary for it to run smoothly. Instead of parts A and B, we can substitute two A parts or two B parts and everything will work just fine. Satan can and will twist and distort anything and everything good which God has designed and created, but he cannot destroy the original blueprint. Have you ever used a machine or device for which you did not have the instruction manual, and while you could get it to function to some degree, you could just tell something wasn't right? The machine didn't seem to be working as efficiently as it should, and there were sections or parts that didn't seem to be useful for anything but must be designed for something. In the same way, in spite of all of society's confident insistence that the family can be anything we want it to be, there is a nagging reminder that Somebody designed this relationship, and it will never function properly except in the way fashioned by the Designer.

Source: Building Christian Relationships: Adult Teacher's Insights, page 56.