> Not sure how you got from "let's encourage fathers and mothers to stay together to raise children with better outcomes" to "seeking discrimination as a policy goal"
Whether it's primarily by gender composition or by biological relationship, what you are proposing is strictly additional discrimination over the alternative you asked to be justified of supporting two-parent families generally and without discrimination among them.
As such, you should bear the burden of supporting that additional discrimination as desirable, rather than your interlocutor bearing the burden of justifying its absence as desirable.
