To keep a constant population or you end up with a bubble. What people also don't realize until they think about it is that you want a higher rate as that means

To keep a constant population or you end up with a bubble. What people also don't realize until they think about it is that you want a higher rate as that means higher probability that there will be people funding your social security when you are older. That requires 2.2 in the USA and rates like 1.5 mean a bubble of older people and not enough paying in.