Earlier quoted context omitted.
Relatively few people's economic output can compare with them producing new people. If your last name is not Feynman or Curie your most valuable contribution to the society is a couple of kids.
Counterpoint - the best single thing you can do for the planet, in terms of minimising your consumption / ecological footprint, is to not spawn.
What I would like to see is a norm on numbers of children. Personally, I think that having more than the replacement number - i.e. more than 2 - is straightforwardly unethical given the stress our planet is under. But by the same token, 2 or fewer is fine. And it would be nice if those who choose to have none got a little more respect for it.