More to your point, there were no little individual nuclear families raising their kids outside the community.
And dont go inventing rights....'every kid has a right to a mother.' I'm sure every kid that's parent has died feels that way. I'd like to think every kid has a right to raised in a loving and secure home and not give a damn about how that was accomplished.
What are they going to do at adoption agencies: Have a line up of babies and the ones not picked by hetero couples go to the gay couples? Do single heteros get to 'pick' before the gay couples? Before single gays? Shall we start a caste system there? All adoptive parents are interviewed and qualified for fitness, period.
Even the straight couple marriage scenario often ends in divorce, abuse, neglect, etc. Even tho differently structured families may have their challenges, it's well proven that single parents, gay couples, families with adopted children, ect...all can raise happy well-adjusted kids...it's about committment, not biology.