The world is full and we don't need more people here.

Eradicating natural sperm would be a good thing. 1) It would reduce the population and 2) it would make sure that those who want to have children can do it only by artificial means and thus their suitability for parenting can be vetted.

After that we can establish a worldwide 0-1 child policy. Tax reliefs to those who choose not to have children and strict vetting process for those who want to have one.