This is a continuation from
yesterday's post. My comment passed the moderators and now appears on the web page, however, I wanted to preserve it here as well.
Your argument that a lack of biological tie between parent and child implies the relationship is artificial would invalidate the entire history of adoption were it true. Therefore I fail to see how a multi-parent household "can only be detrimental." And not to belittle the healthy effects of good economic standing, that is far from the only benefit. A multi parent household, much like your "Aunt Sue" scenario above, gives added emotional support and feedback to the child(ren). Also, having another person with whom to share responsibilities, from feedings to soccer practice drop offs, can reduce stress levels to the benefit of the entire family.
Increased emtional support and decrased levels of stress seem to me to be very much in line with what is best for a child, in every "proper sense."