I predicted long ago I felt this (multi-parent families) was the natural progression of how this would play out in the long-run.  Mark my works that it's just a matter of time before the stigma of polygamy is broken down - and those against it are labeled closed minded and conservative traditionalists. If cultural/biological norms no longer matter, there really is no compelling argument for "a child needs two parents" or "a child needs a father and a mother" as long as it's a loving environment. And finally, 4 in 10 marriages end in divorce so I suspect you won't be gaining wide support for your premise there either.