Although I disagree with the malthusian view on the world I still think there is a more important quantitative argument against this viewpoint. A fertility rate significantly below 2 results in an exponential decline in the population with a lag. In other words, fertility rates close to 1 (as seen in japan and korea), result in a sharp population decline a few decades later that could destabilize the society. Even if I concede the anti-human argument I don’t think the environment would benefit from a destabilizing population collapse. A slow gradual fall with rates close but not quite 2 seems like a much better alternative.