I understand what you're saying, and certainly in today's society with it's legal and social definitions, you are correct. However, I think frannyblue's point was that "convention" needs to be expanded, so that the social laws/mores and legal structure are made to support what we define as unconventional now.

Another example of this kind of thinking: Statistically, gay people have higher rates of depression and suicide. Is this trend inherent to gay people, or do we set them up for failure since our legal system undermines their status, and society defines gender roles in such a way as to exclude them from fitting into convention?

Similarly, if we work to define "family" and "parent" more broadly and set up our legal system to support families, plural, as opposed to only 1 kind of family, who's to say that biological parents would be ideal; As a person who is adopted, I can definitely say that it is totally possible for 2 unrelated people to love and raise a child, and quite well.

Until we define parents as people committed to raising a child, instead of depending on superfluous status in regard to people's gender, preference or couplehood we will be undercutting the possibility of a new level of parenthood, that of community parenting.