We're up against massive loss of biodiversity, loss of habitable space on the planet, and an enormous amount of human suffering and loss of human life due to the current and future effects of climate change. A smaller population will not solve these problems alone, but it will buy us more time to solve them.

FWIW, I'm not trying to promote anything extreme like population control policies, just pointing out that the current trend of population leveling off is generally a good thing.