I think the argument is that the marginal utility/productivity of a person > the resources it costs to sustain a body, even if that body is minimally productive (i.e. subsistence farmer). I think we're better off trying to improve ratio of estimated 2B subsistence farmers that can be replaced with (generously) 100m farmers + machines, and try to figure out how to improve productivity of rest. IMO there are still so many existing poor people, and for purpose of this argument, non/under-consumers, that there's ample (billions of low HDI/low productive workers globally) of untapped demand that can be uplifted to drive growth in all the big things this article calls for. The argument would be different if global human capita productivity is already optimized/maximized and adding more bodies is the only way to raise ceiling, but we're not even close.