By “subsidizing single motherhood”, the author means government assistance programs like TANF (Temporary Assistance for Needy Families), and SNAP (food stamps), and any other form of financial aid that helps single mothers support their children. They think that by taking these things away, they’ll be “encouraging nuclear families”, but the reality is that it plunges many single mothers into poverty, and incentivizes them to stay in abusive marriages or relationships because there is no help for them outside of that. Vice president-elect J.D. Vance has publicly suggested that kids suffer when marriages fail, even when those marriages are violent (if not explicitly saying women should stay in violent marriages for the sake of their children, as the left is fond of claiming):

“This is one of the great tricks that I think the sexual revolution pulled on the American populace, which is this idea that, ‘Well, OK, these marriages were fundamentally, you know, they were maybe even violent, but certainly they were unhappy. And so getting rid of them and making it easier for people to shift spouses like they change their underwear, that’s going to make people happier in the long term.’ And maybe it worked out for the moms and dad, though I’m skeptical. But it really didn’t work out for the kids of those marriages.” [Source]

Seems to me, however, that’s EXACTLY what he’s at least implying. And what of deadbeat dads who don’t want to be involved with their children? Why would you punish those mothers and children? Because punishing women is part of the appeal of these policies, for them. And has no needy family with a father figure ever existed? Has there never been a single father? Why are we singling out women when we’re deciding we’re denying needy people help?

Full contextual analysis of Section 3: The General Welfare here.