It could be a bad thing in the medium term if the number of older people requiring care overwhelms the ability of societies to provide (given fewer working age

It could be a bad thing in the medium term if the number of older people requiring care overwhelms the ability of societies to provide (given fewer working age people contributing). In the longer term, yes, sustainable population certainly seems like a good thing. (Although one could make a utilitarian argument that as long as it _is_ sustainable, and assuming people's lives are generally good, you want as many people as possible.)