I never wanted kids and it looks to me like the last thing this planet needs is more humans. So as part of my personal environmental responsibility plan I am doing the one thing which will have more impact than all the other decisions I could make combined - having no kids.
^^This.
Personally I'd like to see a world in greater balance where the number of births equals (or is less than) the number of people who pass away. Then, rather than development being necessary to continually accommodate all the new people, it could be more focused on improving life for the population already here.
Rather than sprawl and continuing to build new tracts of dwellings, new schools, new infrastructure, for example, resources could be spent improving what we already have.
This is not to say stop making new people, just do it in a more sustainable way. Presently, the world's population doubles what, every 50yrs?
I'm willing to relinquish my single baby quota to another couple who feels they must procreate beyond theirs.