I don't know that a child's lack of a parent of the same gender is as devastating as you make it out to be. I'm male and was raised by two lesbian women of different races. My biological mother is white and had me through artificial insemination with my nonbiological black mother. I lived with the two of them up until I was 7 and they split up, somehow mutually agreeing that I'd live with my biological mom and visit the other on weekends (they weren't married because this was a gay relationship in the 90s to early 2000s).

Not long before I started hitting puberty, my biological mother started sitting me down to watch educational videos, or would push me to read through books with her about how male and female bodies mature. I think this was pretty smart of her for the circumstance.

I now live with my nonbiological mother and am attending college. I think I've turned out pretty well. Looking back on my childhood I don't think I was influenced negativity by the relationship of my parents, or by the absence of a father/father figure. The closest I've gotten to wishing I had a father was when I was very young, spent the night at a friend's and thought their dad was really cool, but ultimately that's only because I thought their dad in particular was really cool, so I never lingered on the thought.

I agree with you to some degree that a child being able to relate to a parent of the same gender can be important, but I don't know that the absence of that interaction is as bad as you make it out to be. However, I think it's also worth adding here that both my parents work in the medical field, so that history of biology probably helped them raise me in ways most same-sex parents don't have the benefit of doing.