This is part of a whole thing where the journalist keeps presenting their framing without question.

Yuuup, and at no point is it explicitly mentioned that what they're doing is entirely unfeasible on a societal level. How on Earth will a couple dozen rationalist having 4, 7, or even 11 kids make up for the hundreds of millions of women in America having 1.5? Or the billions of women having under 2.1 kids in the rest of the world.

On top of that, they only have 3 kids and they've already put a shit ton of time and sunk themselves over half a million in debt just for housing and childcare. I absolutely believe these two can afford it, but this isn't something most Americans can achieve, much less most global families. One couple trying to outfuck global population decline would be like if I tried to end global poverty by becoming really, really rich.